Welcome to the forum. Although you can post in any forum, the USA forum is here in case of local regs or laws
- Thread starter Reddwarf4ever
- Start date
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
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
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
- May 23, 2015
- 35,144
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
Turn the boiler temp down from 72 to 65 or even 60 make sure your how water cylinder is 60dc tho
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.
Last edited:
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 ?
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 ?
Last edited:
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.
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....
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....
Last edited:
- May 23, 2015
- 35,144
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
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.
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.
"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.
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.
Last edited:
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
Last edited:
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.
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.
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 ???
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 ???
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 🤯
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 🤯
- May 23, 2015
- 35,144
- 1
- 14,996
- 113
- Member Type
- Heating Engineer (Has GSR)
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 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.
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.
Last edited:
Official Sponsors of Plumbers Talk
Similar plumbing topics
We recommend City Plumbing Supplies, BES, and Plumbing Superstore for all plumbing supplies.