Central heating pump sizing

[Reddwarf4ever]

Your old pump isolating valves are probably 1/4 turn ball valves that you shut with a screwdriver (slot) or a allen key, nothing sticks out, but unfortunately they almost always leak after operation, you can easily buy new ones with gate valves.

It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.

https://evosta.dabpumps.com/wp-content/uploads/2019/03/Evosta-2-3-Installation-and-Operation-Manual_UK.pdf

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.... some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage 🤯 so assume PSD is owned by Stuart plumbing.....must be offering competition to their own company.....marketing strategy 😎 the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term....

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner.....so much easier with a handle......maybe will replace them when I change the pump 🤔

 

[SJB060685]

John what would happen to the watts display if there was a pump problem or restriction in the system?

 

[John.g]

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.* some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage 🤯 so assume PSD is owned by Stuart plumbing.*.must be offering competition to their own company..marketing strategy 😎 the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term.

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner..so much easier with a handle...maybe will replace them when I change the pump 🤔

You have the correct type isol valves as the gland nut can be tightened up if any leak, so no need for renewal.

Would suggest constant pressure, either CP2 or CP3 see below, answer to SJB.

 

[John.g]

John what would happen to the watts display if there was a pump problem or restriction in the system?

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.
you will see that on constant pressure CP3 that the pump will maintain 4.8M from 0 flow, if the system demand is 1 m3/hr 16.7 lpm then the pump power is 35w, if a restriction in the system and the flow fell to zero then the power is 16.5w and so on in between. more later

 

[SJB060685]

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.

Which chart am I looking at?
Through common sense I imagine if there was a restriction on PP then the pump would modulate down and display a lower wattage?

 

[SJB060685]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something 👍

 

[Reddwarf4ever]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something 👍

I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult......it’s not rocket science.....so we‘ll get there 🙏 keep asking questions, it’s the only way to learn.....also when people understand something so well it’s sometimes easy to downplay an answer.....I will persevere, I want to understand this.....trouble is the pump I ordered has lots of options so need to understand that also, just hope the others are patient with me 🤞

 

[John.g]

Thanks John. As I said the other day, the ins and outs of pumps is new to me, so still trying to figure the charts. I understand what you said above but feel free to share more in case I missed something 👍

Page 25 shows two graphs the top one is the normal pump curves and I am just assuming that you have choosen the pump to run on setting CP3 and just suppose that your system will circulate 16.67 LPM at this setting of 4.8m. if you look vertically downwards you will see another graph of power vs flow for all the different pump settings, you have choosen CP3 and because the system is circulating at 16.67 LPM then the pump power required is 35W, if the system, say boiler Hx starts getting dirty/fouled then the pump speed will reduce to maintain this constant head of 4.8M and if it got completely blocked the pump will still maintain 4.8m but with no flow and still require 16.5W. If you had a smaller system in that even when spotelessely clean only circulates 8.3 LPM (0.5m3/hr) then you can see that the pump only requires ~ 25.5W at the constant pressure of 4.5M.

If you take my system as a example which circulates ~ 15 LPM (0.9m3/hr) @ 3.5M.......I could set the pump to CP2 which is constant pressure at 3.8M, my system would then circulate 15.7 LPM (0.94 m3/hr) @ 3.8M.
with a power demand of 26W.

I woud suggest CP2 (3.8M)as a reasonable starting point, it can very quickly be changed especially with all the info that will be displayed on this pump.

 

[SJB060685]

I am in the same boat as you, things are always so complicated until you understand them, then you wonder why it was so difficult...it’s not rocket science..so we‘ll get there 🙏 keep asking questions, it’s the only way to learn..also when people understand something so well it’s sometimes easy to downplay an answer..I will persevere, I want to understand this.***.trouble is the pump I ordered has lots of options so need to understand that also, just hope the others are patient with me 🤞

My background is oil fired appliances, thats all we were, burner technicians. The system side of things is not something we did much of, so this last year I've been studying and learning a lot of new things to better my understanding. I have a passion for learning and a desire to at least have a good understanding in all areas of heating systems. John here has taught me a few things that I didn't know before joining this forum and to be honest, when it comes to pumps he's probably one of the best on here.

 

[Reddwarf4ever]

John what would happen to the watts display if there was a pump problem or restriction in the system?

Hi
i can only relate to my experience in the oil industry ( Mobil Coryton refinery ) when the pump discharge was shut back ( or there was another restriction to flow ) on a centrifugal pump the Amps ( power ) would drop off, as the pump would just be stirring the liquid and not doing any real work......not sure if that’s applicable, but IMO should be....

 

[John.g]

That would be pretty correct, all very large centrifugal pumps are started with the discharge valve shut to avoid the motor tripping on overload, the discharge vale is then opened gradually.

 

[SJB060685]

Page 25 shows two graphs the top one is the normal pump curves and I am just assuming that you have choosen the pump to run on setting CP3 and just suppose that your system will circulate 16.67 LPM at this setting of 4.8m. if you look vertically downwards you will see another graph of power vs flow for all the different pump settings, you have choosen CP3 and because the system is circulating at 16.67 LPM then the pump power required is 35W, if the system, say boiler Hx starts getting dirty/fouled then the pump speed will reduce to maintain this constant head of 4.8M and if it got completely blocked the pump will still maintain 4.8m but with no flow and still require 16.5W. If you had a smaller system in that even when spotelessely clean only circulates 8.3 LPM (0.5m3/hr) then you can see that the pump only requires ~ 25.5W at the constant pressure of 4.5M.

If you take my system as a example which circulates ~ 15 LPM (0.9m3/hr) @ 3.5M.***...I could set the pump to CP2 which is constant pressure at 3.8M, my system would then circulate 15.7 LPM (0.94 m3/hr) @ 3.8M.
with a power demand of 26W.

I woud suggest CP2 (3.8M)as a reasonable starting point, it can very quickly be changed especially with all the info that will be displayed on this pump.

Thanks again John. I've checked everything against the charts and did the maths for your bottom paragraph and it all adds up. Thanks for taking the time 👍

 

[John.g]

I'll go through another two settings, constant curve (CC) and the most interesting one of all, proportional pressure (PP) control, based on my own system, tomorrow.

 

[SJB060685]

I'll go through another two settings, constant curve (CC) and the most interesting one of all, proportional pressure (PP) control, based on my own system, tomorrow.

Please do. I have a basic understanding i believe but I'm sure you'll teach me otherwise lol

 

[John.g]

Ok, at tremendous expense here are a few numbers/attachments based on my requirements of 15 LPM @ 3.5M head and also based on the TRVs closing down with flow demand as low as 5 LPM.

speed2 will give 16 LPM@4M and 29.5W
speed2 will give 5 [email protected] and 27.5W

CP2 will give 15.9 [email protected] and 26W
CP2 will give 5 [email protected] and 17W

PP3 will give 16.8 [email protected] and 30W
PP3 will give 4.5 [email protected] and 12W

PP2 would almost do the job, [email protected] and (only) 12.2W.

 

[John.g]

Don't seem to be able to attach other file above so attached it here, but can't.
Its zipped excel file so don't know why not.

 

[SJB060685]

Thanks John. Could you give me a quick explanation from your view of CC, CP and PP please.

 

[John.g]

CC or constant curve or fixed speed, the pump runs at a constant speed, the faster the speed the greater the head, all pumps have 3 CCs to cater for different size systems, the problem is the power consumption is almost constant because as the heating (flow) demand goes down due to zone vale closing or TRVs throttling in the pump head increases and the pump efficiency falls off as you can see by the tiny differences in the power consumptions between 15 LPM and 5 LPM.
CP or constant pressure is one of the best controls, the head stays constant due to the pump speed changing up/down to maintain the same head for different flowrates and gives big energy savings like above. 17W vs 26W.
PP or proportional pressure control can give the biggest savings of all as the pump (speed) and head decreases as the flow demand decreases, unfortunately because of the limited number of settings one sometimes has to select a higher setting than necessary like above, where PP2 falls just short of the required flowrate but only consumes 12W, the reason I choose the Wilo is that the PP settings can be incrementally changed in 0.1M stages to give any flowrate required.
Also PP control reduces the (speed) head as the flow decreases, and vica versa unlike the CC settings.

 

[SJB060685]

Thanks John for a clear explanation. One last stupid question. I take it long before the introduction of erp products and modulating pumps all circulating pumps were just CC?

 

[John.g]

Correct,

 

[John.g]

still can't attach zipped file.

 

[Reddwarf4ever]

Haven’t installed my new DAB EVOSTA 3 Replacement Grundfos Circulating Heating Pump 21412 yet, waiting for the milder weather, wonder if anyone knows of a way I can measure the boiler inlet temperature? It’s displayed in the boiler, but accessed via keypad, would like permanently displayed so can check its blow 55oC.....need a sensor wire with a gauge thanks

 

[Reddwarf4ever]

i installed the new DAB 3 pump today.....have been in touch with DAB for guidance, but terminology seems to fluctuate between website, instructions and received emails....reference to constant speed & pressure seem get mixed up.....I have been advised to set at constant curve setting @ speed 3 is maximum as a starting point.

think this is the TOP symbol....getting 33-35W 5.4-5.6m & 0.7m3/Hr flow....sometimes it slows down ??? Got no one to help me and watch the boiler, so can onot relate what the pump is doing......I tried Heating + Hot water and Hot water only and readings were the same. Leaving it here for now and monitoring the boiler DT....in the past few days it got worse, outlet temp of 72oC was only achieving 55oC return temperature...so was struggling to keep the boiler in condensing mode..... o idea why the DT had moved away from 20oC.....

I really hope this pump will resolve my problems, not sure if the top option is the best for

 

[ShaunCorbs]

Turn the boiler temp down from 72 to 65 or even 60 make sure your how water cylinder is 60dc tho

 

[John.g]

i installed the new DAB 3 pump today..have been in touch with DAB for guidance, but terminology seems to fluctuate between website, instructions and received emails....reference to constant speed & pressure seem get mixed up..I have been advised to set at constant curve setting @ speed 3 is maximum as a starting point.

think this is the TOP symbol....getting 33-35W 5.4-5.6m & 0.7m3/Hr flow....sometimes it slows down ??? Got no one to help me and watch the boiler, so can onot relate what the pump is doing...I tried Heating + Hot water and Hot water only and readings were the same. Leaving it here for now and monitoring the boiler DT....in the past few days it got worse, outlet temp of 72oC was only achieving 55oC return temperature...so was struggling to keep the boiler in condensing mode.. o idea why the DT had moved away from 20oC.***.

I really hope this pump will resolve my problems, not sure if the top option is the best for

There seems to be a fair bit of resistance to flow, however, letting that aside for the moment then from your numbers above, Flowrate 0.70 M3/hr (11.7LPM), deltaT 17C? (72-55) Boiler output = 11.7*60*17/860, 13.88 kw, so as long as the min output of the boiler is > this then there should be no problems. However if you wish to get the return temp down then do as suggested.... reduce the boiler SP. Personally,I don't like running circ pumps (especially A rated ones) flat out, its up to yourself but if you were to consider changing the pump mode to constant pressure , CP3 = 4.5M then you should get a flow rate of 0.63 M3/hr (10.6 LPM) (& 27W) and a slight increase in the boiler deltaT, you can then reduce the boiler SP to suit yourself but remember this will also reduce the rad output/boiler demand and you don't want ro reduce it below the boiler minimum output, can't remember if you have that min output for that boiler?.

If you wish to calculate the boiler output yourself while testing its.... KW = (M3/hr)X60X16.66XdeltaT/860.

 

[Reddwarf4ever]

Looks like there is a 60 minute time out to do editing, which is a pity.

UPDATE
1- I have set the boiler to 18KW, first time ever....its modulating ok, but have had to reduce the target temperature to 68oC to keep the inlet below 55oC.....so quite a low DT
2-occasionally the pump declares ‘LO FLOW’ then shortly after shuts off, restarts with the same message, then after a few minutes reverts to the previous readings I.e. 0.7m3/Hr etc....set it to heating only for now to establish that works ok.

not sure if the higher flow; which it looks like I have, has dislodged some debris and causing the pump problems.....or it’s something else, all rads now very hot, even one in a room which previously struggled to get warm. Ideally want to heat the hot water in the day, together with the heating, as on hot water only, I don’t think I will get a low enough inlet temperature for condensing.... going to try again tomorrow....also if I try to heat the hot water on its own, not sure if the DT between the immersion cylinder and boiler outlet is enough

thanks for the replies......very confused about the pump setting options., is CP3 the middle icon of the three ..?.....happy to have a lower flow if it helps the DT....will look at the charts again...

still worried about the LOW FLOW message, although hasn’t happened since a few hours ago....🤞

also was considering increasing two lounge rads from single to double, won’t increase the flow obviously bit will emit extra heat and help the boiler DT, any thoughts ?

 

[John.g]

The pump shouldn't be displaying that message except its some form of protection, suggest changing to CP3 for now, you can see the different mode symbols on top and the 3 vertical bars are the settings for each mode.

 

[Reddwarf4ever]

Ok I set the pump to D3, the boiler is now at 11KW ( although it’s modulating there is no indicator of actual KW ( Gas ) being burnt.....dropped outlet temperature to 68oC and return @57oC just checked outside and it’s Not condensing.....can’t drop,outlet any more, don’t think it will manage Hot Water at such a low temperature.....should I try D1 ? What is the theory about having a lower flow Vs inlet temperature ? Is it simply it has more residence time in the rads ? Any thoughts on upgrading 2 rads 100cm x 50cm to double fin ? Can’t see it will hurt 🤔

been told power flush devices can be hired, will have to drain down in the summer if I fit new rads, could do it then......don’t want to do it if not needed though

P.S. I forgot to say I accidentally left hot water & heating on together, although this should be acceptable to do, have now left it on heating only....

 

[ShaunCorbs]

is the system hot already or cold ?

 

[John.g]

What do you mean by D3 on the pump, is it constant pressure as shown in the diagram, and can you read off the flowrate, the head and the watts, can then calculate the boiler output.

And yes your old pump was kaput or full of sludge as it should have been circulating 0.66 M3/hr (11 LPM) at a head of 4.9M based on your new pump readings above.

 

[Reddwarf4ever]

What do you mean by D3 on the pump, is it constant pressure as shown in the diagram, and can you read off the flowrate, the head and the watts, can then calculate the boiler output.

And yes your old pump was kaput or full of sludge as it should have been circulating 0.66 M3/hr (11 LPM) at a head of 4.9M based on your new pump readings above.

Sorry

meant CP3, trying CP2 now.....will get readings ASAP

 

[John.g]

"What is the theory about having a lower flow Vs inlet temperature ? Is it simply it has more residence time in the rads ? "
More sometimes equals less.
Yes, but you also need to keep the mean radiator temperature as near design temperature as possible, above you have flow/return temps of 68/57, mean of 62.5C which results in the rad emitting 81% of its rated output based on a room temperature of 20C, if you are happy with this but require a return temperature of say 50C but also require the same mean rad temperature of 62.5C then there is only one way of achieving this and that is to raise the boiler/rad flow temperature to 75C and keep reducing the flowrate until the return temp is 50C, this still gives a mean rad temp of 62.5C. and no problems in heating your DHW cylinder.

 

[Reddwarf4ever]

"What is the theory about having a lower flow Vs inlet temperature ? Is it simply it has more residence time in the rads ? "
More sometimes equals less.
Yes, but you also need to keep the mean radiator temperature as near design temperature as possible, above you have flow/return temps of 68/57, mean of 62.5C which results in the rad emitting 81% of its rated output based on a room temperature of 20C, if you are happy with this but require a return temperature of say 50C but also require the same mean rad temperature of 62.5C then there is only one way of achieving this and that is to raise the boiler/rad flow temperature to 75C and keep reducing the flowrate until the return temp is 50C, this still gives a mean rad temp of 62.5C. and no problems in heating your DHW cylinder.

Thanks, will experiment with your suggestions tomorrow...defo looks like this pump is doing a much better job than the old one......If CP1 doesn’t give a low enough head to achieve a good DT, is there another setting to try ?
1- does anyone know if the heat recovery is a constant, as the inlet temperature falls ? Or as I assume it’s a curve, giving less heat recovery as the temperature falls, think the majority must be achieved at around 50-55oC ?
2-I read it’s a good idea to increase rad sizes when changing to a condensing boiler to assist the low return temperature, so is my idea of changing the 2 rads in my lounge to double fin, a good way to go ?
3- is it normal to heat the hot water the same time as having the heating on ? Because the heat removed from the immersion cylinder will be no where near what the rads remove, and having both would ‘ share’ the flow....
4-.I assume in the summer months with hot water only, condensing mode would not easily be achieved

 

[Reddwarf4ever]

is the system hot already or cold ?

HOT 🔥

 

[John.g]

I would increase the flow temp to 75C then go to CP2 and write down the boiler deltaT and the pump flow,head & watts.
Then ditto for CP1, PP3 & PP2.
Remember though that if the head is too low then some rads will run colder than others and require balancing, for the moment don't bother with balancing.
I run my boiler at 75C with TRVs on 8 of the 10 rads and I've often seen 40C return temps, I have never balanced the rads, I run on PP3 which, with my system, gives ~ 12LPM @ 3.4M head. I would expect your system to run at [email protected] on CP1, 8.5LPM@3M on CP2, [email protected] on CP3. 9 [email protected] on PP3, & [email protected] on PP2.

Q1. If you mean boiler heat recovery = efficiency then the lower the return temp the greater the efficiency due to enhanced condensing effect.

Q2. I have used a factor of X2 on any replacement rads to allow for weather compensation etc if my present non condensing boiler ever gives up the ghost.

Q3. A lot of boilers now use DHW priority where, when DHW is required, the boiler switches to HW heating and automatically increases the boiler SP temp to 80C which gives very fast heating times but little or no condensing benefit and then switches back to CH after the 30/45 mins or so required.
But if you are not too worried about the length of time required to heat the cylinder then you can install a balancing gate valve on the cylinder return and by throttling it in to say 1/4 turn open you can easily get 50C for a lot of the heating period even with a flow temp of 75C.

Q4. As above.

The effect of return temps on condensing benefit is clearly shown below, not any huge benefits at 50/55C but below 50C, not bad at all.

Happy testing.

 

[John.g]

Condensing Effects on boiler efficiency.

 

[Reddwarf4ever]

Thanks that graph is exactly what I was looking for, even asked in a scientific forum, but got no where 🤯
trying various options with the boiler

CP1 Boiler target 68oC 8KW limit inlet 46oC
8.6-10W
1.8-2.0m
0.4l/h

CP2 Boiler target 68oC 8KW limit inlet 46oC
13.2-17W
2.6-3.0m
0.5-0.7l/h
not sure why the fluctuation, found if impress the Mode button once quickly, it cycles through the values, the manual says pressing it changes the mode, but only when it’s displaying the mode ( multipurpose buttons not helpful ) I previously held the button in until it displayed a rotating ‘arrow’ then pressed once, but although it display the readings, it had gone through a degas so values had changed, easier now I know.

One problem IMO apart from the pump, is the valiant boiler Eco tec plus 418, it does not modulate very well, often continuing to hard fire as it reaches the target temperature and thus overshoots, made worse by the fact it cuts out when only 3oC over temperature. Takes a long while going through the tripping restarting before it settles down again. Sometimes I drop the KW limit to 5KW and ‘ nurse ‘ it back up by slowly increasing the KW.....IMO I should t have to do this, & if I can do this then the boiler should. I wonder if the boiler is actually oversized, which again antagonises the problem. if it were sized as say 12 KW instead of 18 KW, wouldn’t it be able to cope with lower flows ? If that is the case then it will always be a struggle.....

I have 7 radiators which could be made double fin.....wonder how much effect that would have on the delta T ???

 

[Reddwarf4ever]

Ok on CP1... pump 9W 1.8m 0.5l/h fairly stable
boiler 68oC target & actual, inlet 55oC

So am just on the condensing temperature & it’s slowly going up.
i have 12 rads total
All 100x50cm
downstairs
2 double ( one of which only gets really hot when on CP3 in extension room)
2 single
1 towel
upstairs
2 towel
5 single

Detached brick house built 1987, 3 bed, game room, store room, lounge, kitchen, cloakroom, bathroom and shower room....usually at 23oC, wonder what size boiler I would need for this, need to compare with the 18KW I have.

wonder if, as per my previous post, the boiler is over sized, assuming a smaller one can handle a lower flow, which would help the DT.....all I can think of doing at this point is increasing rad sizes.....or living with an inefficient heating 🤯

 

[ShaunCorbs]

As you can adjust the output of the boiler work out your rad kw and add them all together that’s what you set your boiler out put to

 

[John.g]

I don't see any reason whatsoever to get a smaller boiler, you already have a 5.5kw (minimum output?) boiler, you seem to have some control problem when first firing up, either not modulating down rapidly enough after ignition (unlikely, with the boiler demand above of 10.23 kw on CP1 and 15.34kw on CP2, OR it is modulating down OK after start up but is then increasing the firing rate too fast to enable it to ramp down when the SP is reached, not helped by the 3 deg hysteresis.
You might carry out a simple test, once the boiler has settled down at its target temperature of 68C?, change the target temperature rapidly to say 73/75c and see if the burner cuts out on high temp (target+3C, in your case), if it does. then a control problem, IMO, or it may cut out on deltaT so make a note of whichever, if satisfactory, reduce the target to 68c and again watch its reaction.

 

[Reddwarf4ever]

As you can adjust the output of the boiler work out your rad kw and add them all together that’s what you set your boiler out put to

I can’t actually adjust the output, only limit the maximum.....can’t forever keep adjusting it, which is what I am doing now.....have to find a website to help me calculate the rad KW consumption....unless you know of one ?

 

[Reddwarf4ever]

I don't see any reason whatsoever to get a smaller boiler, you already have a 5.5kw (minimum output?) boiler, you seem to have some control problem when first firing up, either not modulating down rapidly enough after ignition (unlikely, with the boiler demand above of 10.23 kw on CP1 and 15.34kw on CP2, OR it is modulating down OK after start up but is then increasing the firing rate too fast to enable it to ramp down when the SP is reached, not helped by the 3 deg hysteresis.
You might carry out a simple test, once the boiler has settled down at its target temperature of 68C?, change the target temperature rapidly to say 73/75c and see if the burner cuts out on high temp (target+3C, in your case), if it does. then a control problem, IMO, or it may cut out on deltaT so make a note of whichever, if satisfactory, reduce the target to 68c and again watch its reaction.

Will do as you suggest.....it’s all driving me mental......had really hoped the new pump would solve my problems......I turned on hot water, while the boiler was firing steadily, the firing increased slightly, due to the cylinder demand.....left it alone, but after a while it started cutting out on over temperature.....and went into its usual cycle.....the cylinder temperature was increasing, had hoped it would be ok.....now turned off the hot water and the boiler is firing ok....it’s at 7KW 68oC inlet 43oC, bit only because it has been cycling for an hour or more....so for some reason it doesn’t like heating and hot water on together.....I can’t restrict the inlet flow to the cylinder as if on HW only, the boiler would have, I assume an insufficient flow......

the boiler does have an option for a separate HW control, just needs a valiant module, can’t find any info on that....have emailed vailiant....so if I can get some sort of stability in the day with the heating ( miracles do happen ) then can allow the HW to heat overnight with the higher temperature set for HW.....

thanks for all the continued support.......my Wife says my life has been taken over trying to get this boiler sorted...

😎😎😎

 

[ShaunCorbs]

I can’t actually adjust the output, only limit the maximum..can’t forever keep adjusting it, which is what I am doing now..have to find a website to help me calculate the rad KW consumption....unless you know of one ?

screwfix book find your existing rads roughly they list the kw output on there website

and yes you need to set the maximum to this value

I would stagger hot water times roughly an hour earlier than heating in the morning

 

[Reddwarf4ever]

I don't see any reason whatsoever to get a smaller boiler, you already have a 5.5kw (minimum output?) boiler, you seem to have some control problem when first firing up, either not modulating down rapidly enough after ignition (unlikely, with the boiler demand above of 10.23 kw on CP1 and 15.34kw on CP2, OR it is modulating down OK after start up but is then increasing the firing rate too fast to enable it to ramp down when the SP is reached, not helped by the 3 deg hysteresis.
You might carry out a simple test, once the boiler has settled down at its target temperature of 68C?, change the target temperature rapidly to say 73/75c and see if the burner cuts out on high temp (target+3C, in your case), if it does. then a control problem, IMO, or it may cut out on deltaT so make a note of whichever, if satisfactory, reduce the target to 68c and again watch its reaction.

Well I increased the KW to 15 or the boiler wouldn’t be able to increase firing, set output to 75oC climbed to 78oC and cut out......reduced KW to 7 as before changed outlet to 68oC and it cut out at 71oC.....even at only 7KW.....😩 waiting for it to ‘ settle down ‘ again

 

[Reddwarf4ever]

screwfix book find your existing rads roughly they list the kw output on there website

and yes you need to set the maximum to this value

I would stagger hot water times roughly an hour earlier than heating in the morning

Thanks will have a look.....going to run hot water 4am to 7am.....when the heating is off.....but will need to change outlet temperature to 75oC for the night and back to 68oC for the day....

 

[ShaunCorbs]

Well I increased the KW to 15 or the boiler wouldn’t be able to increase firing, set output to 75oC climbed to 78oC and cut out...reduced KW to 7 as before changed outlet to 68oC and it cut out at 71oC..even at only 7KW.***.😩 waiting for it to ‘ settle down ‘ again

this is normal if the system is hot

 

[Reddwarf4ever]

Well as expected the boiler ‘settled down’ again and is currently set at 6KW outlet temperature 68oC inlet 52-53oC......going to leave this alone and see how it goes tomorrow, will see if it heats up the hot water tonight, but suspect I will need to change the output temperature to around 75oC.....

don’t think it’s raising the house temperature much, but comfortable, hopefully long term if I change all the single rads to double, it will give the boiler more to work on.

 

[ShaunCorbs]

The output temp doesn’t have that great effect on room temp unless your running the room temp at your flow temp

 

[Reddwarf4ever]

The output temp doesn’t have that great effect on room temp unless your running the room temp at your flow temp

Sorry don’t understand that.......

 

[John.g]

I can’t actually adjust the output, only limit the maximum..can’t forever keep adjusting it, which is what I am doing now..have to find a website to help me calculate the rad KW consumption....unless you know of one ?

Well as expected the boiler ‘settled down’ again and is currently set at 6KW outlet temperature 68oC inlet 52-53oC...going to leave this alone and see how it goes tomorrow, will see if it heats up the hot water tonight, but suspect I will need to change the output temperature to around 75oC..

don’t think it’s raising the house temperature much, but comfortable, hopefully long term if I change all the single rads to double, it will give the boiler more to work on.

You said in one post that you have to run on CP3 to heat up all the rads and would suggest that you run in this mode for the time being at any rate.
What mode is giving you the above numbers?.

There is clearly something wrong with the boiler as you shouldn't have to keep chasing the output up/down to get the boiler to run, IMO you should be able to leave it at max output, I can understand setting the CH output to say 20kw on a 36kw combi with a heating load of 18kw, otherwise not.
You might consider getting a fixed price (if they provide this type of service) from vaillant to fix this boiler.

 

[Reddwarf4ever]

You said in one post that you have to run on CP3 to heat up all the rads and would suggest that you run in this mode for the time being at any rate.
What mode is giving you the above numbers?.

There is clearly something wrong with the boiler as you shouldn't have to keep chasing the output up/down to get the boiler to run, IMO you should be able to leave it at max output, I can understand setting the CH output to say 20kw on a 36kw combi with a heating load of 18kw, otherwise not.
You might consider getting a fixed price (if they provide this type of service) from vaillant to fix this boiler.

Complained about this from dat one, but said nothing wrong, put me off Vailant I can tell you....using CP1 with the above figures......

 

[John.g]

Complained about this from dat one, but said nothing wrong, put me off Vailant I can tell you....using CP1 with the above figures.***.

Well, that's one reason for having to limit it to 6kw as the flowrate on CP1 is only 6.7 LPM and with the stated deltaT of 16C gives a boiler output of 7.5KW. All gas boilers fire up initially with a output of ~ 70% = 12.6kw on your boiler (limiting output has no effect on fire up, for stable ignition ) so a flowrate of 6.7 LPM and 12.6kw will result in a deltaT of 27C, very close to the deltaT limit of 30C, also, a higher flow will result in slower flow temperature rise which will help to prevent the boiler reaching (SP+3C).
CP3 at 10.5 LPM will only result in a deltaT of 17C on fire up and IMO the pump should always be run at this flowrate and should certainly allieviate some of your problems, must bear in mind that most system boilers with internal circ pumps will generally run with a flowrate at least as high as this on a 18kw boiler.
Once your HW cylinder is heated up in the morning you can then reduce the boiler flow temp to give ~ 50C return temperature.
You may also find now on CP3 that the boiler will supply both CH and HW without tripping.

 

[John.g]

A few other things have come to mind, if, which I think you have, a open vented system, you might check that there is no pump over through the vent above the F&E (feed and expansion) tank, on CP3 or higher, and also obviously that it contains water.
If you have a mid position diverter valve then the water can recirculate on pump overrun.
the default overrun time is 5 mins, you might reduce this to 2 /3 mins and the default anti cycling time is 20 mins, assume you have reduced this to something like 3 mins. The table below shows anti cycling times but afraid I can't interpret it, any ideas?.

 

[Reddwarf4ever]

A few other things have come to mind, if, which I think you have, a open vented system, you might check that there is no pump over through the vent above the F&E (feed and expansion) tank, on CP3 or higher, and also obviously that it contains water.
If you have a mid position diverter valve then the water can recirculate on pump overrun.
the default overrun time is 5 mins, you might reduce this to 2 /3 mins and the default anti cycling time is 20 mins, assume you have reduced this to something like 3 mins. The table below shows anti cycling times but afraid I can't interpret it, any ideas?.

A few other things have come to mind, if, which I think you have, a open vented system, you might check that there is no pump over through the vent above the F&E (feed and expansion) tank, on CP3 or higher, and also obviously that it contains water.
If you have a mid position diverter valve then the water can recirculate on pump overrun.
the default overrun time is 5 mins, you might reduce this to 2 /3 mins and the default anti cycling time is 20 mins, assume you have reduced this to something like 3 mins. The table below shows anti cycling times but afraid I can't interpret it, any ideas?.

A few other things have come to mind, if, which I think you have, a open vented system, you might check that there is no pump over through the vent above the F&E (feed and expansion) tank, on CP3 or higher, and also obviously that it contains water.
If you have a mid position diverter valve then the water can recirculate on pump overrun.
the default overrun time is 5 mins, you might reduce this to 2 /3 mins and the default anti cycling time is 20 mins, assume you have reduced this to something like 3 mins. The table below shows anti cycling times but afraid I can't interpret it, any ideas?.

View attachment 47252

I couldn’t make any sense out of this table either 🤯 yes it’s open vented & the feed & expansion are joined together...yes I have a 3 port diverted valve.....will give this a few days to stabilise.....then try CP2......this morning the heating came on at 68oC with an inlet of 53oC set at 7KW, modulating lovely, all rads hot 🔥 if I change the two lounge rads from single to double, that may reduce the inlet temperature 2-3oC or will allow me to run at 70oC......which will be better for HW heating in the night....although as an experiment I turned on the HW this morning, after showers & the boiler temperature initially took a dive and the inlet temperature dropped to 45oC, the temperature gauge at the stat has risen from 25oC to 39oC so it is heating....boiler has now re established at 68oC with an inlet of 51oC so its modulating ok and heat still being transferred to the HW cylinder.....🤞 the cylinder reaches at least 44oC ( prefer 48oC )which gives 55oC at the top.....looking good so far....🙏 anti cycling and over run now reduced to 3 minutes thanks for explaining the 70% fire rate for initial startup, that helps in my understanding

View attachment 47252

A few other things have come to mind, if, which I think you have, a open vented system, you might check that there is no pump over through the vent above the F&E (feed and expansion) tank, on CP3 or higher, and also obviously that it contains water.
If you have a mid position diverter valve then the water can recirculate on pump overrun.
the default overrun time is 5 mins, you might reduce this to 2 /3 mins and the default anti cycling time is 20 mins, assume you have reduced this to something like 3 mins. The table below shows anti cycling times but afraid I can't interpret it, any ideas?.

View attachment 47252

 

[John.g]

On CP1??.
When you first installed the Pump you ran on full speed and your were able to up the rating to (where it should be) 18kw, CP3 should, more than likely achieve the same and just maybe CP2.

I know Vaillant arn't very helpful but i would ask them why the flow temperature hysteresis of 3C is so low and if it can be adjusted.

 

[Reddwarf4ever]

On CP1??.
When you first installed the Pump you ran on full speed and your were able to up the rating to (where it should be) 18kw, CP3 should, more than likely achieve the same and just maybe CP2.

I know Vaillant arn't very helpful but i would ask them why the flow temperature hysteresis of 3C is so low and if it can be adjusted.

Have emailed valiant about the hysteresis ( a new word I have learnt 👍 ) as everything is running nicely at CP1, would like to keep it there for at least a week, so I know I have somewhere to go back to 🤞 also at CP2 and especially CP3 the return temperature was rather high, non condensing. But will try next week.

 

[Reddwarf4ever]

Just got an SF.H flashing, found a post from kevindgas, 2011 with how to reset by pressing + & - together, well it worked 👍 couldn’t find reference to this error anywhere else on the internet, states it’s a Service Code, should I worry ??? Thanks

 

[ShaunCorbs]

Due for a service ?

 

[Ben-gee]

There’s a lot to be said for boilers that don’t give any information to end users...😈....💣

 

[Reddwarf4ever]

Maybe, but it’s good to know what the problem is.....

 

[John.g]

Have emailed valiant about the hysteresis ( a new word I have learnt 👍 ) as everything is running nicely at CP1, would like to keep it there for at least a week, so I know I have somewhere to go back to 🤞 also at CP2 and especially CP3 the return temperature was rather high, non condensing. But will try next week.

You mentioned increasing the rad sizes so I came up with the following numbers based on that., I based them on doubling the rad outputs but can calculate it for any increase you want.
Based on your actual results it seems that you have a a relatively small installation with total rad output of ~ 9 kw.
If you look at the 9kw base below (top row) you can see that your actual output is 6.73kw with a return of 52C. If you were to increase (second row) the flow rate (CP2/CP3) to 0.63M3/hr to keep the boiler happy then by reducing the flow temp to 60C you will still get a return of 52C BUT a reduced output of 5.87kw, you would againthen need to up the flow temp on HW.

If you now doubled the rad outputs to 18kw, again with a happy boiler flowrate of ~ 0.6M3/hr, you can see the effect of different flow temps on rad output etc, if you select a flow temp of 60C then you will get a return of 44C and a output of 10kw, you would need to up the flow temp on HW.
If you select a flow temp of 72C then you will get a return of 52C and 14.35kw output and so on.

Table Below might be of some help.

​	​	​	Flow​	Return​	DeltaT​	Boiler​	Boiler​	Boiler​
​	​	​	Temp​	Temp​	Temp​	Output​	FlowRate​	FlowRate​
​	Deg rad​	Output​	Deg.C​	Deg.C​	Deg.C​	KW​	LPM​	M3/hr​
9KW Base​	40​	75%​	68​	52​	16​	6.73​	6.03​	0.36​
​	36​	65%​	60​	52​	8​	5.87​	10.52​	0.63​
​	​	​	​	​	​	​	​	​
18KW Base​	32​	56%​	60​	44​	16​	10.08​	9.03​	0.54​
​	38​	70%​	68​	48​	20​	12.60​	9.03​	0.54​
​	42​	80%​	72​	52​	20​	14.35​	10.28​	0.62​

 

[Reddwarf4ever]

You mentioned increasing the rad sizes so I came up with the following numbers based on that., I based them on doubling the rad outputs but can calculate it for any increase you want.
Based on your actual results it seems that you have a a relatively small installation with total rad output of ~ 9 kw.
If you look at the 9kw base below (top row) you can see that your actual output is 6.73kw with a return of 52C. If you were to increase (second row) the flow rate (CP2/CP3) to 0.63M3/hr to keep the boiler happy then by reducing the flow temp to 60C you will still get a return of 52C BUT a reduced output of 5.87kw, you would againthen need to up the flow temp on HW.

If you now doubled the rad outputs to 18kw, again with a happy boiler flowrate of ~ 0.6M3/hr, you can see the effect of different flow temps on rad output etc, if you select a flow temp of 60C then you will get a return of 44C and a output of 10kw, you would need to up the flow temp on HW.
If you select a flow temp of 72C then you will get a return of 52C and 14.35kw output and so on.

Table Below might be of some help.

​	​	​	Flow​	Return​	DeltaT​	Boiler​	Boiler​	Boiler​
​	​	​	Temp​	Temp​	Temp​	Output​	FlowRate​	FlowRate​
​	Deg rad​	Output​	Deg.C​	Deg.C​	Deg.C​	KW​	LPM​	M3/hr​
9KW Base​	40​	75%​	68​	52​	16​	6.73​	6.03​	0.36​
​	36​	65%​	60​	52​	8​	5.87​	10.52​	0.63​
​	​	​	​	​	​	​	​	​
18KW Base​	32​	56%​	60​	44​	16​	10.08​	9.03​	0.54​
​	38​	70%​	68​	48​	20​	12.60​	9.03​	0.54​
​	42​	80%​	72​	52​	20​	14.35​	10.28​	0.62​

Thanks that’s defo given me something to think about and work on....currently I a, using CP1 @7KW inlet 53oC & flow temperature 66oC the house is slowly heating up, I set the HW to come on 2 hours before the heating goes off at 10pm and 3 hours in the morning when the heating goes on at 7am....this achieved 47oC at the cylinder stat, which I know is around 60oC at the outlet, unfortunately although the boiler modulates really well, every so often, 1-2 hours it cuts out, I can only assume ( don’t suppose these boilers have an event log 🤞 ), that it’s over temperature maybe it climbs to 69oC if a TRV changes up or down, I suppose 🤔 if it had a 5oC tolerance instead of 3oC maybe it would manage.....when it cuts out, I set the flow temperature to 85oC ( max ) when the gas firing starts reducing again, the temperature drops to 60-65oC & i then set the flow temperature back to 66oC and it starts modulating again.....will try the other ideas soon.....

thanks

 

[John.g]

If the TRVs are of the manual type, like mine, they should give pretty good modulating control as against on/off even though they have a very small hysteresis (in Air) of 1 to 2C, also when setting up I find that even a difference of 0.2/0.3 on the index makes a big difference to the room temperature, all of mine (8) are set to between 1.8 and 2.2 to give ~ 18C to 22C room temperature and with a boiler flow temp of ~70C (OF boiler, cutin/cutout 75C/65C) quite regularly give return temps as low as 40C, oil fired boilers have no problems in dealing with very high deltaTs and even though they run flat out all the time and are constantly cycling, the 20/25 litre heat exchanger acts as a buffer so no cut on flow temp cut out on firing up.
I have read of some on/off and other control problems with the programmable TRVs.

 

[John.g]

Thanks that’s defo given me something to think about and work on....currently I a, using CP1 @7KW inlet 53oC & flow temperature 66oC the house is slowly heating up, I set the HW to come on 2 hours before the heating goes off at 10pm and 3 hours in the morning when the heating goes on at 7am....this achieved 47oC at the cylinder stat, which I know is around 60oC at the outlet, unfortunately although the boiler modulates really well, every so often, 1-2 hours it cuts out, I can only assume ( don’t suppose these boilers have an event log 🤞 ), that it’s over temperature maybe it climbs to 69oC if a TRV changes up or down, I suppose 🤔 if it had a 5oC tolerance instead of 3oC maybe it would manage..when it cuts out, I set the flow temperature to 85oC ( max ) when the gas firing starts reducing again, the temperature drops to 60-65oC & i then set the flow temperature back to 66oC and it starts modulating again..will try the other ideas soon.***.

thanks

Even though I would be surprised if any of the TRVs are doing much controlling with the house not fully heated, it is possible, and if so, to help avoiding this annoying 2 hourly cut out you might consider changing to PP2, this, by my calculation, should give you very close to the present performance on CP1 but may well help to smoothen out the flowrate if these TRVs are inclined to hunt.

 

[Reddwarf4ever]

Thanks John, currently I am running the Boiler at 66oC, @7KW with a typical return temperature of 52-53oC. It’s modulating very well & the house does get up to 22.5oC ( I actually set the room stat to 23.5oC during 7am to 10am & and the boiler goes off, which allows the rads to cool down and improve the return temperature when the boiler restarts) I set the heating to come on at 7am which goes off at 10pm. Have set Hot water to come on at 7am to 10am & 8pm to 10pm this manages to keep the Hot water at a good temperature, also it heats the water while the heating is on & in condensing mode. If I increase the pump pressure / flow and have to lower the flow temperature, I will have problems with Hot water heating. Don’t have separate controls and settings for heating and hot water and would be ***bersome to keep changing the boiler flow temperature.

I will try PP2 and see how that performs

 

[Reddwarf4ever]

Thanks John, currently I am running the Boiler at 66oC, @7KW with a typical return temperature of 52-53oC. It’s modulating very well & the house does get up to 22.5oC ( I actually set the room stat to 23.5oC during 7am to 10am & and the boiler goes off, which allows the rads to cool down and improve the return temperature when the boiler restarts) I set the heating to come on at 7am which goes off at 10pm. Have set Hot water to come on at 7am to 10am & 8pm to 10pm this manages to keep the Hot water at a good temperature, also it heats the water while the heating is on & in condensing mode. If I increase the pump pressure / flow and have to lower the flow temperature, I will have problems with Hot water heating. Don’t have separate controls and settings for heating and hot water and would be ***bersome to keep changing the boiler flow temperature.

I will try PP2 and see how that performs

For some reason the pagelayout using safari has got reallybad, is in Columns tried Firefox and ok, wonder if can be fixed? Looks like all the adverts causing it

 

[John.g]

I just go back to new posts to display the full page or something like that.

 

[Reddwarf4ever]

Oddly enough, the webpages are displaying ok today open safari, must depend on which adverts are running 🤔 the DAB 3 evosta pump I received did NOT have the foam insulation shroud that I saw in a YouTube installation video and assumed it would be included any thoughts ?

 

[Reddwarf4ever]

Just had a reply from DAB, despite it showing this pump with the insulating shroud, all over their website, apparently it’s not on the model I bought, even though it’s a DAB 3 and can’t be bought separately.....although another online retailer said I can buy it for £29 + VAT plus £4 delivery, quite expensive for a piece of foam 🤯 will use my hessian wrap from the old pump, not so pretty but effective.....don’t see why DAB couldn’t just send me one out......

 

[Reddwarf4ever]

I tried PP2, but the boiler seemed to be cutting out more, not sure if fluctuations upsetting it, as it only has a +3oC Flow to Actual tolerance, maybe this is the reason, still waiting for Vailant to respond about if it should be +5oC 🤔 trying CP2 at the moment, has been behaving very well on CP1, but one radiator only barely gets warm, it’s in a downstairs extension room, maybe it’s a plumbing problem 🤯 but on CP3 it certainly got hot....

thanks

 

[John.g]

The reason the rad is not circulating is probably that CP1 is limited to a 1.8M head which realistically is a bit low, CP2 at 3M should be a good compromise to get circulation, theoretically, at least, the flow rate should increase from 0.4 m3.hr to 0.52 M3/hr and you may be able to nurse another few kw from the boiler without cut out. CP3 at 4.5M is probably the best choice, hydraulically, you may loose a few % in boiler efficiency but maybe a small price to pay for comfortable heating until Vaillant respond.

 

[Reddwarf4ever]

The reason the rad is not circulating is probably that CP1 is limited to a 1.8M head which realistically is a bit low, CP2 at 3M should be a good compromise to get circulation, theoretically, at least, the flow rate should increase from 0.4 m3.hr to 0.52 M3/hr and you may be able to nurse another few kw from the boiler without cut out. CP3 at 4.5M is probably the best choice, hydraulically, you may loose a few % in boiler efficiency but maybe a small price to pay for comfortable heating until Vaillant respond.

Thank you CP2 did work reasonably well, the ‘ problem rad ‘ began to warm up. I then switched to CP3 and the ‘ problem rad ‘ is now very hot, can still keep my hand on it just....the other rads are really hot, the one next to my Wife’s chair is too hot too touch, with the Boiler flow set at 64oC however the return temperature has now increased to 56oC 🔥 Might leave it at CP2, where the return was 51-53oC 🥶 the ‘ problem Rad ‘ is not so important, as it’s in the ‘ ‘game room’ not used very much. Probably need a CP 2 1/2 🤔, since increasing the flow from CP1 to CP2 and more recently CP3 the boiler is modulating a lot better, hasn’t cut out at all yet. Also the Hot water heated from 7am-11am & 8pm to 10pm is working very well, with CP1 & 2, Will be a different story in the Summer months when it will be Hot Water only.....

 

[ShaunCorbs]

Have you tried balancing the rads more with more pressure you will need to close the lockshields more

 

[Reddwarf4ever]

Have you tried balancing the rads more with more pressure you will need to close the lockshields more

only three can be adjusted, the other 9 all have TRVs....will have a look, thanks

 

[ShaunCorbs]

only three can be adjusted, the other 9 all have TRVs....will have a look, thanks

the other side should be a lockshield valve you can adjust that

 

[Reddwarf4ever]

the other side should be a lockshield valve you can adjust that

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

 

[ShaunCorbs]

cant see the point in restricting the lock shield when the TRV is designed to control the room temperature, or am I missing something ?

the lockshield controls the return temp

you should be getting around 10dc drop through the rad

 

[John.g]

Thank you CP2 did work reasonably well, the ‘ problem rad ‘ began to warm up. I then switched to CP3 and the ‘ problem rad ‘ is now very hot, can still keep my hand on it just....the other rads are really hot, the one next to my Wife’s chair is too hot too touch, with the Boiler flow set at 64oC however the return temperature has now increased to 56oC 🔥 Might leave it at CP2, where the return was 51-53oC 🥶 the ‘ problem Rad ‘ is not so important, as it’s in the ‘ ‘game room’ not used very much. Probably need a CP 2 1/2 🤔, since increasing the flow from CP1 to CP2 and more recently CP3 the boiler is modulating a lot better, hasn’t cut out at all yet. Also the Hot water heated from 7am-11am & 8pm to 10pm is working very well, with CP1 & 2, Will be a different story in the Summer months when it will be Hot Water only.***.

What was/is the pump head and flow on CP2 & CP3? , theoretically PP3 should give somewhere in the middle, by my calculations, but your numbers will tell us more.

 

[Reddwarf4ever]

CP1 10W 1.8m 0.4m3/hr
CP2 17W 3.0m 0.7m3/hr
CP3 30W 4.5m 0.9m3/hr
PP3 26W 4.1m 0.8/m3/hr - 0.9m3/hr

CP3 gives a good flow, all rads very hot, but inlet temperature >55oC
CP2 All rads hot except one, which is warm, inlet temperature 52-53oC
CP1 all rads hot except one barely warm, inlet temperature 52-53oC

trying PP3

believe the flow is a ‘ calculated’ one, can’t see how they could fit a flow meter inside the pump....with pump head and watts it’s an easy calculation.

DAB going to send me a ‘ spare’ heat shroud they found. They say the manual and website is for the European model not the UK one....how I am supposed to know that is beyond me.....think for the few pence it costs, all their pumps should have this....

thanks

 

[John.g]

CP2, CP3 & PP3 are doing as I would have expected.
The pump actually only uses the power and pump+motor efficiency to calculate the head and flowrate, it knows which mode/head is selected and can then derive the actual head/flowrate, the clever part IMO is how it derives the pump+motor efficiency for every single point on all the curves. Some hold that it is only a approximation especially on some of the UPS models and it may well be but before I installed my Wilo Yonos Pico, I just connected it up to a a gravity feed with a gate valve on the discharge and measured the flowrates for a number of different operating modes and it seemed to be within 5 to 10% of what the pump curves showed for the displayed power consumptions, (I don't have head & flowrate displayed.), so all in all a good aid to navigation IMO. You can also estimate it (the flowrate) from the (clamped) boiler output and deltaT.

 

[John.g]

Should also maybe pointed out advantage of PP mode with reduced flow demand say if TRVs shutting in, if the flowrate demand halved from 0.9 to 0.45m3/hr on CP3 then the head would still remain at 4.5M but on PP3 would reduce to ~ 3.3M with lower pump power required and less throttling of the TRVs.

 

[Reddwarf4ever]

Should also maybe pointed out advantage of PP mode with reduced flow demand say if TRVs shutting in, if the flowrate demand halved from 0.9 to 0.45m3/hr on CP3 then the head would still remain at 4.5M but on PP3 would reduce to ~ 3.3M with lower pump power required and less throttling of the TRVs.

Thanks for the explanation. Running PP3, the boiler is 63oC limited to 8KW, getting return temperature 54-55oC ( getting steam from the boiler vent, so must be condensing ) ALL rads currently 🔥 even the problem one, boiler modulating well. Guess this is the best I can get at the moment, Hot water heating perfectly using the times I have set. Would love to get a better efficienc, but compared to my old pump with a flow temperature of 75-78oC ( god knows what the inlet temperature was then 🤯 ) I must be saving £££s Think my best plan is to upgrade the two lounge single rads to double fins ( Summer job, need modify the tail feeds with a bend, have a bender, but not done that before ) then I may see the inlet temperature fall a few degrees.

thanks so so much for all the help and support, it’s been invaluable.

P.S. another massive advantage of fitting the DAB 3 is that it’s so dam quiet, Never know it’s on, previous pump could always be heard.

 

[John.g]

Don't know if Vaillant came back to you yet but spoke to a friend of mine who has a 20kw Vokera Mynute, he watched the flow temperature rise from boiler fire up at 42C to its target temperature of 55C, it rose fairly rapidly until ~ 52/53C and then gradually increased to and settled at its target temperature of 55C.
When boiler/system was running for ~ 20 mins he increased the target temp from 55C to 60C, the temperature exceeded its target by 3C briefly and then settled down at 60/61C.

 

[Reddwarf4ever]

Don't know if Vaillant came back to you yet but spoke to a friend of mine who has a 20kw Vokera Mynute, he watched the flow temperature rise from boiler fire up at 42C to its target temperature of 55C, it rose fairly rapidly until ~ 52/53C and then gradually increased to and settled at its target temperature of 55C.
When boiler/system was running for ~ 20 mins he increased the target temp from 55C to 60C, the temperature exceeded its target by 3C briefly and then settled down at 60/61C.

No they haven’t, considering phoning them, assuming I can get a technical answer to the trip setting.....I am certain it shouldn’t be +3oC.....thanks

 

[Reddwarf4ever]

have a reply from Valiant

“”As you already have the permanent 230V supply and the pump wired to the boiler for the pump over run, all you will require is twin core from the boiler ebus connection to the VR66 and sensoCOMFORT RF receiver, Are these devices installed in the boiler cabinet or remotely ? If within the boiler cabinet, then the cable run will be minimal, does that make sense ? the sensoCOMFORT and outdoor sensor are both wireless. The zone valves and hot water cylinder sensor connect to the VR66. Don’t want an outdoor sensor, if the VR66 is in the boiler cabinet ( kitchen ) don’t see how the How water sensor connects to the VR66 at the boiler ??? Didn’t get a price, which I asked for ??? “”

Said the boiler should go off when 5oC above flow temperature, I replied it’s always been 3oC, not sure how this can be fixed, also modulation is poor, often overshoots many times before stabilising....usually need to do manually to get it to settle......asked if this can be changed or fixed “”

The boiler turning off is controlled by the return temperature, as the return temperature gets closer to the flow temperature the burner modulates, when the return temperature gets to 5 degrees below the flow temperature the boiler turns off then goes into pump over run and anti cycle time. If the heat can’t leave the boiler quickly enough it will shut
down when it reaches the target flow temperature or it may over shoot. This cannot be adjusted.

https://www.wolseley.co.uk/wcsstore7.00.1066.986/ExtendedSitesCatalogAssetStore/images/products/AssetPush/DTP_AssetPushHighRes/std.lang.all/ti/on/Vaillant_vr66_Installation.pdf

 

[John.g]

Been reading a few bits and pieces re this target temperature and from what I can gather it might be set at say 75C but the flow temp might only be 50C depending on the flow/return deltaT and the setting D.00 which can be either on Auto or manually selected to the maximum kw required and setting d.17, flow/return regulation which I interpreted should be set to flow regulation if you want flow temperature control, might be worth carefully noting these parameter settings before making any changes.

 

[Reddwarf4ever]

D17 is accessed via the 2nd diagnostic level. I have entered this via D97. D17 is displaying 0....only has 2 options 0 or 1....will need to get info on these ‘extra’ settings.
running D0 with 11KW, seems to prevent some of the cycling due to poor modulation when first firing up, but ok once stabilised and also from cold, seems a happy medium 🤞don’t think I really need the V66 module & all the complications & expense. Hot water managing ok for now, so it’s just the summer months to see how I will need to set it. Maybe 62oC as a target temperature will be ok with 2 periods per day, the Hot water should be cool at these times and may even go into condensing mode, if not will raise the target temperature to suit. Might not be able to achieve condensing mode with Hot Water only in the summer months.....will all be a distant memory in the not too distant future when we heat using Electricity 🤯. Just wish I could get the 3oC changed to 5oC for the over temperature cut out.

 

[John.g]

The +5C temp cut would certainly help but I feel that you havn't got true control of the flow temperature, its well named as target temperature, vaillant state that its the return temperature (probably the deltaT) that modulates the boiler, IMO Flow temperature control allows the flow temperature to increase very rapidly and as it approaches the SP temp it reduces the firing rate (derivative control) to avoid any or very little overshoot, this is what I see happening on my relations 20 kw Vokera VisionS where even with a 5kw demand and no range rating the flow temp only overshoots by ~ 2C. and the settles down but it has that +5C margin.

 

[Reddwarf4ever]

The +5C temp cut would certainly help but I feel that you havn't got true control of the flow temperature, its well named as target temperature, vaillant state that its the return temperature (probably the deltaT) that modulates the boiler, IMO Flow temperature control allows the flow temperature to increase very rapidly and as it approaches the SP temp it reduces the firing rate (derivative control) to avoid any or very little overshoot, this is what I see happening on my relations 20 kw Vokera VisionS where even with a 5kw demand and no range rating the flow temp only overshoots by ~ 2C. and the settles down but it has that +5C margin.

Hello
tHank’s “ derivative control” haven’t heard that term for a long while, used to try and ‘ help out’ the instrument mechanics when tuning refinery process controllers, fascinating stuff. Found these two settings in the 2nd level diagnostics, wonder if it’s to do with derivative control ?

need to try and stop it overshooting.....

 

[John.g]

No idea re above, I wouldn't touch it.

Wonder are there any readers here with vaillants that work like a normal boiler.

 

[Steel Buttocks]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

 

[Reddwarf4ever]

Open the gate valve fully on the cylinder return. Check all TRVs are fully open or remove a few of the heads. Slow down the pump speed. Check pump valves are fully open. Then try again. If problem persists, i would remove and inspect pump.

It’s a brand new pump & working very well, the main issue is with the boiler controls.....

 

[John.g]

Some very interesting comments in this blog, also explains anti cycling time tables.

Vaillant cycling problem

Vaillant 400-series boilers cycle on and off rapidly when they shouldn't - the stories of their unhappy owners

vaillantcyclingproblem.blogspot.com

 

[Reddwarf4ever]

Hello
read through it all, makes me wonder if Vailant wasn’t the best choice.
as an update, I am now running at 11KW limit, seems to satisfy fast warm up from cold and doesn‘t seem to impact on a boiler restart. Target temperature 62oC and is hot enough to keep the Hot water hot, set for Hot water, 8PM to 830PM and 8AM to 11AM Pump still on PP2, working well, all Rads getting hot. Room stat gets satisfied 2
-3 times a day, allowing the boiler to go off.....so the only thing I need to really resolve is the 3oC hysteresis rather than the 5oC that Vailant say it should be and the over enthusiastic firing amd overshooting.....hoped the heating curve settings could be the solution to this......

 

[John.g]

PP2?? or PP3.

 

[John.g]

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

 

[Reddwarf4ever]

PP2?? or PP3.

Yes PP3.....

A recent post I saw somewhere re a Glowworm "low water pressure" alarm on boiler/pump start up got me thinking about your very first post paragraph re S.53 & S.54. The glowworm alarm (and start inhibit?) is triggered by a pressure sensor which detects the small rise in pressure when the circ pump starts, so obviously if the pump doesn't start or is fouled with sludge etc then this alarm annunciates, the glowworm sensor apparently can get blocked very easily and a temporary fix was to increase the filling pressure and might lead one to falsely believe that this sensor was only used only as a method of detecting sufficient water in the boiler.
Valliant informed you that S.53 is triggered by the 30C flow/return deltaT but I think its triggered by the above (borne out by changing the pump) and S.54 is the deltaT alarm, however if this is correct then the boiler would have to fire up, perhaps on minimum firing?, to enable the high deltaT to develop between the flow/return or else S.54 isn't configured quite correctly. (Or else the boiler just waits and waits to see if S.53 clears).

I also see that you can run the boiler on return temperature by changing d.17, even though you seem to be getting very satisfactory performance now it might be interesting to try this control mode sometime to see its effect on the target (flow) temperature and of course condensing benefit, it is primarily suggested for UFH.
Also may be worth checking that d.18 (pump overrun) is on its default setting 1 ( comfort or continuous running).

Strange, but in all those interesting blog posts I havn't seen it mentioned anywhere that the flow trip is SP+5C.

Hi
fascinating, as Spock would say, I still believe S53 is caused by a 30oC temperature differenc, as I used to run the output at 75-78oC, where it regularly exceeded the 30oC difference......this hasn’t happened once now, as I rarely see a differential that high, typically 20oC Max......D17 is I believe for underfloor heating systems, will have a look, but as you say, it’s running so well now, can’t see how I can improve it, but will give it a go, in the interest of science 😂 will check D18....I also haven’t seen any reference to the +5oC cut out, but have an email from Vailant confirming this, so hopefully it’s correct, just need to find out how to fix mine from 3oC to 5oC....🙏

take care. 🙏

 

[John.g]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

 

[Reddwarf4ever]

Looks like temperature derived so, I,ve seen that it sometimes displays with deltaTs as low as 22/23c so perhaps looks at the rate of rise of the flow temperature as well, anyway not a problem for you now.

Cant believe how silent the boiler and pump are, modulating perfectly @ 62oC DT 11-12oC inlet 52oC house warming up all rads hot......never ever been this good
had problems since 2009 🤯 before that my Potterton Netaheat presented no problems, but at 60-65% efficiency wasn’t good.
to save me looking back, was there a calculation for KW being used by the boiler, based on flow / DT maybe ?
Also on a bit of an off topic subject, I have a room stat a Coronado controls 2005 model, it has an ‘ offset ‘ setting of 0.5 or 1.0.....but with a target of 22.5oC it switches on @ 21.5oC and off @ 22.2oC don’t see this makes sense the ’offset’ is set at 0.5.

wonder if it’s faulty or I have misunderstood how it should work.....gets quite cool ( need to keep warm for my Disabled Wife ) before it switches on again....thanks

D18 is set to 0 ( zero ) what would changing it to 1 mean ?

 

[John.g]

The calc for KW is, KW= m3/hr*16.66*60*deltaT/860. = 0.85*16.66*60*12/860, 11.86KW.

This the ref I have to D.18. (1 is the default)