twin boiler install - this cant be right can it??

[CChris]

Hi,

As a homeowner and not a plumber, Ive got a question regarding the way my new twin boiler system has been set up. Before I start giving the plumber twenty questions and suggesting he hanst done the job right, would anyone be able to advise on this setup:

I have two 30kw boilers, I preferred this setup rather than going for a single commercial size boiler, but I dont think that the two boiler system has been set up correctly. Im leaning toward the plumber forgetting to install two check valves.

Heres a rough diagram of what I have set up on the wall.



Pumps are integrated within the boilers.

At present, we're just running the one boiler, though the idea is that both would be on, and by setting thermostat down on one and up on the other we can switch between which is doing the lions share of the work - changing it over every now and them to prevent uneven wear on one boiler.

With one boiler off (simulating what would happen in the event of a failure), Ive observed the following when the system starts up from cold:

Heat flows out of boiler 2 as expected (pipe is getting hot). This then flows down toward the zone valves and depending on which part is calling for heat, the pipes in this direction get hot. (though the electrician appears to have wired the downstairs and upstairs zone valves in parallel and no matter which zone calls for heat both the upstairs and downstairs loops open... prat.)

However, what also happens is that the flow pipe toward the switched off boiler gets hot, then the return pipe leading to the switched off boiler, and ultimately back to the return of the firing boiler.

This takes as little as a minute, so it would appear that the flow is forcing its way in the wrong direction through the switched off boiler, and straight back to the return. This results in the firing boiler switching off quite often, and well before the temp of the return pipe leading back from the zones is anywhere near hot.

Ive also done a test by turning the isolating valves off that are part of the switched off boiler and then follwed the heat from cold. In this scenario the heat flows out to the zones, but the pipes to and from the switched off boiler remain cold - therefor forcing all the heat into the system where it is required.

So, am I correct in assuming the plumber has simply missed a couple of check valves from the connections between the boilers?

 

[gassafe]

A picture of the install may be easier to comment on as it would show pipe sizes & if its been teed in equally...

When connecting two boilers I have normally seen it done through a low loss header, with external pumps, rather than your system with 2 pumps which would be pumping the sample pipe... I'm not sure about the check valves, I wouldn't think there necessary...

Someone more experienced about connecting a system your size will be along later...

 

[CChris]

Will be able to get a pic later.

Though I believe it's 22mm from boilers to a 35mm run which then tees to 22mm for first floor and another 22mm pipe which is then itself teed to feed the rest.

There are no external pumps other than the one which does a hot water loop, this is on separate timer clock/plug to allow hot water circulation beyond the actual heating cycle.

 

[Unregistered]

can a stopcock be responsible for the banging I get when I turn off my cold water tap, can not find any lose pipes and the bang seems to be coming from the stopcock.

 

[ShaunCorbs]

What boilers you got ?? And yes it could be a jumper on the stop tap that's making the noise

And how big is the property ??

 

[oz-plumber]

You are correct in what you are saying.

The boilers need to have check valves installed so that the heating water is not short circuited through the idle boiler.
You will also need an external by-pass valve installed so that when the zones valves shut the pump can still push water around a circuit. Most boilers have internal by-passes integrated into the boiler, but its generally required to have an external bypass.

 

[ShaunCorbs]

Well I would install a swing check valve

 

[Deleted member 25704]

For these types of installation, manufacturers such as Vaillant, have provided system diagrams and wiring diagrams to help. Hence, my first action would be to consult the manufacturer and ask them to send you a suitable system and electrical diagram for linking two boilers. In the past I have installed these in this way, which has required a 'reverse return' arrangement, check valves and a MB1 relay to separate the wiring.

 

[CChris]

Thanks for all the info so far.

Boilers are Ideal Logic 30. Still away from the house at the moment so will get a picture up later.

Im also going ahead with a Honeywell EvoHome installation, so it may be the case that some of these valves for the heating will be replaced/removed (or at the least rewired so both floors valves don't open at once when only one calls for heat). This will be a different installer that I have previously used for my office block. (didnt use this installer on the house as plumbing was via a main contractor for the building works we had done).

Hot water gets hot, radiators get hot (though some take ages), so its not a dire emergency, but with winter looming and two children of 3 and under in the house Im hoping to be able to put both boilers in action, which I cant do at the moment due to this reverse flow issue at the moment.

 

[CChris]

What boilers you got ?? And yes it could be a jumper on the stop tap that's making the noise

And how big is the property ??

Sorry missed this, the stopcock question wasnt from myself.

Boilers are Ideal Logic 30, property is around 6500 sqft, (1000 sqft of underfloor), 5 shower/bathrooms.

 

[kris]

Id definitely have a low loss header with the size of the property. Non returns will have to be used however if the system was piped correctly then it should work with out them.
Here's a bit of info about low loss headers and what they do.

https://www.google.co.uk/url?sa=t&s...Z9nDxM&usg=AFQjCNEjImkbOUAn2BviUTLrT4eKwHEY0A

 

[buckley plumb]

Well I would install a swing check valve

Have you got a link for these

 

[stevetheplumber]

ive fitted similar without a low loss and its worked ok does need some thing to stop the flow through the redundent boiler though

 

[ShaunCorbs]

Have you got a link for these

yea np

2" Horizontal Fi Swing Check Valves - SCV100-2 - Supremeplumb.com

and to op do you have any rads or is it just under floor heating????? if so how many plz

as i am thinking maybe the pump is to small

 

[hammers4spanner]

ye gods

This plumbs in for a drilling (sighs)

 

[CChris]

Got 29 radiators in total, though currently 9 not yet connected and a further 5 turned off. So currently running 15 radiators and one section (around 30 sqm) of under floor.

Some radiators still not hot at all. Then it seems like once a couple or more are up to temperature then the trss shut them off and the previously cold ones then get hot and vice versa. Seems like something is not up to the job and that's before we switch on the other 14 rads and under floor heating zone.

I've noticed that the return to the boiler is hot, causing boiler to shut off, but the vastajority of this is heat returned from the underfloor heating manifold as that's only taking a bit. The return from the central heating isn't as hot.

I'll get those pictures shortly.

 

[ShaunCorbs]

Got 29 radiators in total, though currently 9 not yet connected and a further 5 turned off. So currently running 15 radiators and one section (around 30 sqm) of under floor.

Some radiators still not hot at all. Then it seems like once a couple or more are up to temperature then the trss shut them off and the previously cold ones then get hot and vice versa. Seems like something is not up to the job and that's before we switch on the other 14 rads and under floor heating zone.

I've noticed that the return to the boiler is hot, causing boiler to shut off, but the vastajority of this is heat returned from the underfloor heating manifold as that's only taking a bit. The return from the central heating isn't as hot.

I'll get those pictures shortly.

for that and the cylinder and the f=r to the underfloors the stnd pumps wont be enough and with the other problems i would put off the honeywell home install and fix the problems and make sure it works first

 

[CChris]

Honeywell install not scheduled until the end of the month (via a different installer that I have more confidence in )

Though yes I'm hoping to get these issues all resolved before the install of the evohome. I may yet get that installer to cast his eye over this installation first.

I did wonder why there were no external pumps, when I found that they were integral to the boiler, I assumed they would be up to the job or the plumber wouldn't have used them. Seems this may not be the case....

 

[CChris]

Worth adding that the underfloor has its own pump. Would this change the view of pump being inadequate?

Edit: also just found another possible issue. Looks like the trss are shutting off too soon. As an example I've got a cold radiator in a relatively cool area that is set to maximum. Loosen the collar on the trv and I can hear water flowing now.

Are these trv's adjustable in their sensitivity/temperature sensing? I'm wondering if this is half the issue I'm battling.

 

[ShaunCorbs]

Worth adding that the underfloor has its own pump. Would this change the view of pump being inadequate?

Edit: also just found another possible issue. Looks like the trss are shutting off too soon. As an example I've got a cold radiator in a relatively cool area that is set to maximum. Loosen the collar on the trv and I can hear water flowing now.

Are these trv's adjustable in their sensitivity/temperature sensing? I'm wondering if this is half the issue I'm battling.

if poss take all the trv heads off / open them all up and see how they heat up wise and no took that into my thoughts as they have sep pumps and trv/themo/there own controls

any chance you could post some pics up of boilers and if you dont know how to take the heads off post a pic up and we can advise

 

[CChris]

Will have to leave the trv head off test until tomorrow as the kids are asleep and as we don't have carpet down in various areas yet Im likely to wake them clamping around. If they wake up at their usual 5am I'll give it a whirl then! Lol.

Heads come off no problem though so easy enough to do when I have the time. Got photos on the phone so will try and upload, but no pc to make it easy as we're still unpacking after moving back into the home after the building works.

 

[CChris]

In another stroke of genius it appears that the valve to the underfloor heating hasn't been wired in. It was permanently closed. Ffs I'm off to bed with a duvet and the lot shut off until the morning.

Thanks for the help folks. Will let you know how I get on.

 

[CChris]

Pictures and layout diagram as requested.

To be fair the plumber has been a pretty good guy, and has helped out with a lot of other issues which the main builder seemed to want to sweep under the carpet and hide away from me, so Im not wanting to fall out with the guy if there is anything obviously wrong, just looking for second opinions and dont want to make a mountain out of a molehill with the guy.

He called last night after I dropped him a text about the rads not warming up for the kids, and I advised that once ive loosened the collars on the TRV's a little, then things warm up - so it could be overly agressive TRV's causing part of the issue is my thought (which are being swapped when the evohome goes in anyway). The wiring in of the valve to the underfloor is down to the spark, so not attributing this to the plumber.

Anyway, heres the layout and pics - from my amateur untrained eye there doesnt seem to be anything amiss, and plumber advised offset(?) Tees rather than straight tees for the boilers would solve the reverse flow issue?

Thanks again for all the help, it is appreciated.

 

[Mike Jackson]

That layout is just screaming reverse circulation to the heating with the configuration of the returns.

 

[CChris]

That layout is just screaming reverse circulation to the heating with the configuration of the returns.

Can you explain this please? I know a bit, but dont profess to know it all, and dont want to come across that way when talking to the plumber. But any description of the problem would help - thanks 🙂

Im guessing its something to do with the returns from the HW tank and underfloor flowing into the return of the heating circuit. Would this be possible if the valve to the heating were shut at the flow end?

 

[CChris]

I know its replying to my own thread, again, but am I missing a boiler bypass here? if all four electronic zone valves are shut, I see no route to discharge the residual heat. Or am I missing something obvious as a novice?

EDIT: found the following in the installation guide for the boilers:

"However, if the system employs thermostatic radiator valves on all radiators, or two port valves, then a bypass circuit must be fitted with an automatic bypass valve to ensure a flow of water should all valves be in the closed position."

AND

"Systems incorporating zone valves which could completely cut off the flow through the system must also include a bypass."

As I have TRVs on all rads, and zone valves which could cut off the flow in all directions, Im assuming this applies to me and a bypass needs to be fitted?

 

[tolly]

That Primary flow looks 28mm to me, not 35mm like you've written in the pictures?

 

[ShaunCorbs]

not too bad install a few mistakes and tolly is right its 28mm

 

[CChris]

Can you advise on the "mistakes"?

Had the underfloor on for 4 hours now and it's not even thinking about getting warm. Flow pipe to the manifold is hot, return is stone cold. Manifold is warm, two flow pipes to the kitchen zone are also warm, but their respective returns are stone cold. Do the little things in the top of the manifold signify flow rate through those pipes? If so, there's no flow through them.

Yep you are right it's 28mm not 35. Could the 22mm take the theoretical 60kw from these two boilers?

 

[Chalked]

Needs check valves on return. The boilers will develop a pump flow fault, as it will not get a pressure increase on strt up. Caused by one boiler reverse circulating through another..

 

[ShaunCorbs]

Can you advise on the "mistakes"?

Had the underfloor on for 4 hours now and it's not even thinking about getting warm. Flow pipe to the manifold is hot, return is stone cold. Manifold is warm, two flow pipes to the kitchen zone are also warm, but their respective returns are stone cold. Do the little things in the top of the manifold signify flow rate through those pipes? If so, there's no flow through them.

Yep you are right it's 28mm not 35. Could the 22mm take the theoretical 60kw from these two boilers?

the pumps working on the under floor systems? and could you post a pic up as it sounds like a valve is shut/not open full if you have heat by the manifold

 

[buckley plumb]

could need bleeding all air out.

 

[CChris]

Here's the manifold etc. I believe one issue was the zone valve not being wired in for the underfloor heating. It was mostly shut, so very little flow to the manifold, but enough to get the flow pipe hot.

Manually set this to open and flow to the manifold is now fine.

Pump on the manifold appears to be working fine.

I'm only trying to heat one of the two zones controlled by this manifold, that's fed by the two pipes on the right.

I can feel the two pipes get warm, but flow meters on the top only ever show one of them moving, up to about 2l/m the other doesn't budge.

I tested putting the other zone on so that the other 3 pipes were in action, their flow meters didn't move either. Only ever the second one from the right (which can be seen in the picture).

The manifold itself on the flow side got very hot. I'd say not far off the temp of the flow pipe from the boiler. Thermostat on the left set just pas the 40. I assume this can't be right and I most certainly don't want to be sending 80 degree water into the under floor. So switched the lot off.

Any ideas on this one? I seem to be fighting numerous issues here.

 

[Nostrum]

This is why systems get commissioned, why hasn't it been done by the installer?

 

[chris watkins]

I hope you are holding a large retention on the Builder CChris cos you are going to need it to pay for the corrective works.

You have established that it is not working & not installed correctly so strongly recommend that you commission an independent consultant to prepare a report on what is wrong & what will be required to correct this.
I understand you want to find out yourself but with all due respect it is very complicated with all the component bits & how they will work or not together.

Just to answer a couple of your questions from earlier
1. You would need min of 35mm to shift 60kW @ Delta T 20deg C
2. The residual head pressure of the boiler pump in a 30kW boiler is less than 2 Metres this is not enough to overcome the resistance of the system fittings & pipework, hence why you don't have circulation. (you think it is bad now with outside temp of 15deg C just wait till the winter)

Please, I have seen enough of these Builders Plumber Jobs, get a pro in as soon as possible & you may want to sever your links with the installing plumber, I am sure his hart is in the right place but he is out of his depth on this one !!! More than likely he was almost forced to take it on by the builder or he wouldn't get any more work from them.

 

[CChris]

Appreciate the comments. Yes I do want to understand the issues myself but also appreciate that I'm not a plumber, so I'm in no way going to attempt to fix any issues myself or rely solely on answers from here to get things put right (although the advice is very much appreciated).

The under floor has been working. As has the heating. Both at different times and both in "manual" guise. I.e pumps plugged in and a single boiler on the wall etc.

I think the issues have arisen when it's come to sticking the second boiler on and connecting the lot up.

Yes there is still a decent chunk left to pay on the project of circa £30k plus another £4.5k retention, which I have zero intention of paying over until every single aspect has been demonstrated working.

For now the heating and hot water works in a fashion, so not the emergency it could be, but it will be inspected by another installer asap. Most likely the one I have had work on our office block.

You are almost certainly correct with the builder forcing the plumber to do it. This builder has very few contacts as he alienates almost every one he works with, and has been lucky not to wake with a horses head in his bed on this project if I'm honest. Had I not had some knowledge and another builder who has built rental properties for me in the past to call upon, he would have tried to slide some fantastic bodges past me. (Set a lintel too low, just cut the door frame down to suit.... as a minor example)

Really appreciate the input here guys, it is very helpful indeed. Hope I can return the favour somehow. If anyone is in the Chesterfield area and wants to have a look first hand and earn some beer tokens, feel free to drop me a message (apologies if this breaches any forum rules I am unaware of).

 

[stevetheplumber]

its badly undersized 22 isnt going to run even 15 radsyou are definitly going to need a low loss header and some bigger pumps

 

[CChris]

There are 19 rads on the 1st floor and 10 on the ground. Fed by a 22mm circuit to each, with the final connections to each rad being a mixture of 10mm or 15mm depending on their location either in the new or old part of the house (all pipe is new).


Are you suggesting I'm into having them lift the floor and replace all the 22mm run throughout the house?

 

[ShaunCorbs]

There are 19 rads on the 1st floor and 10 on the ground. Fed by a 22mm circuit to each, with the final connections to each rad being a mixture of 10mm or 15mm depending on their location either in the new or old part of the house (all pipe is new).


Are you suggesting I'm into having them lift the floor and replace all the 22mm run throughout the house?

maybe depends on how long the runs are/ how hes piped them

 

[CChris]

maybe depends on how long the runs are/ how hes piped them

I'd say longest run of 22mm is likely 30m or so to the last rad on the run.

As far as I'm aware it's 22mm flow, 22mm return and tees off in either 15mm or 10mm for each individual rad.

I guess all I can do as a basic test is to pop the tops off the trv's on all installed rads (20 out of the 29) and see if I can get them all belting hot in a not unreasonable length of time. If it can do that on one boiler then I'll probably be safe.

Worth adding that it is very unlikely I'll ever want them all on at the same time. Hence the evohome installation. It's more likely that only half the home would be heated at any point in time.

Still, I "should" be able to have them all belting hot at the same time.if I wanted, so it's no excuse for an undersized system if that turns out to be the case.

 

[ShaunCorbs]

I'd say longest run of 22mm is likely 30m or so to the last rad on the run.

As far as I'm aware it's 22mm flow, 22mm return and tees off in either 15mm or 10mm for each individual rad.

for a start them (internal) pumps wont do anything that far you might be ok with the pipe work under the floor but i would recomend on upping where you can see it eg where the boilers are and fit a low loss header and bigger pump/pumps

 

[CChris]

Furthest radiator away from the boiler does get hot though. And fairly quickly. I'll run an acid test with the lot on full bore and see what happens.

 

[ShaunCorbs]

Furthest radiator away from the boiler does get hot though. And fairly quickly. I'll run an acid test with the lot on full bore and see what happens.

its when everything is calling eg underfloor rads cylinder if you can test and turn all of it on go for it

 

[CChris]

I should be able to do that some time tomorrow. Will run off a load of he HW after everyone's showered to make sure the cylinder is also calling when I test.

Though no idea if the under floor is actually doing its job and sucking heat into the slab. Trying to get this to work on its own this evening was a failure.

 

[ShaunCorbs]

Don't have a clue regarding the underfoor as I don't do it maybe ask one of the lads in here if you can manually open it 1/2 to get some heat through it ??

 

[CChris]

Results of test are not good.

Woke to a cold house and no hot water. Boiler showing L1 fault. Overheat lockout.

I'm guessing this is because I closed the valve to underfloor heating and switched that off. As per a previous post there is no bypass as advised in the installation manual. So when the heating shut off last night, all valves were closed and the pump overun had nowhere to go.

Took the opportunity to whip the trv heads off all rads, ensure pin was moving and open the other ends. All rads fully open. Whacked the thermostats up to full and set the hot water on boost. An hour later and some rads are still cold. Notably the furthest ones away.

I accept this is a little unfair test as normally those that have got belting hot like the small one in a walk in wardrobe would have shut off by now and not be taking heat from the system. But still for the furthest ones away to still be cold is not great.

Either pipes undersized or pump not adequate?

As I can get the furthest one away hot if I turn others down, then it seems I can get heat to it, but the pump just isn't capable of doing all the rads at the same time. Does this sound plausible?

Is a low loss header and external pumps the solution? Or is the belt and braces method to uprate the pipes?

Some rads are fed by microbore, 8 of the currently switched on 20. With a further 6 plumbed with microbore but not yet connected. All in 15 plumbed with 15mm and 14 with microbore when all done. Anything untoward here?

 

[chris watkins]

Can I ask where the designs for this system are, the heat loss calculations, pipework sizes etc ? Surely you must have seen these before you employed the builder & the work started.

This is clearly no ordinary 3 or 4 bed semi, so why would not alarm bells not be ringing long before now, you clearly have experience in property development, it just seems very strange why you would just rely on a builder/plumber to provide heating / hot water for such a place.

As before, you now need someone (a design engineer) to come in see what should be there, what has been installed, talk you through the options, prepare a report that you can present to the builder setting out the corrective works required. etc etc. (just withholding money without this is not an option, he will take you to court)

Yes it is going to cost money, with all due respect, it can not be done on a plumbing forum & by you but it sure as hell will cost you a lot more if you don't employ an expert !!

 

[CChris]

Nope not a property developer, just have a builder friend that I've bought houses off plan from and I know it's quality stuff. Sadly he was too busy for my own personal house extension.

I didn't see calcs. Though I'd did design where I wanted radiators. I trusted the builder who has done large commercial stuff before and the plumber to do their jobs. I did not have time to micro manage the build, and as I'm no heating engineer just assumed (there's the big mistake) that these guys knew what they were doing.

I've got ano engineer coming to assess the situation on Monday.

I haven't been living at the property while work has been taking place, so have been unable to test all these elements in any real life scenarios until now.

Done my own totting up of the radiators and it totals 71,592 btu upstairs, before I add on the four large towel rads. I'm going to take a wild stab in the dark that 22mm as a feed to this zone isn't going to cut it.

Fully aware what I'll need to present to the builder. I've asked the plumber for design calcs to prove what was installed was/is correct.

 

[chris watkins]

as a guide (& we work in Watts not BTUs now, have done for 30years)
15mm = 11000
22mm = 23000
28mm = 40000
35mm = 62000
@ delta T 20deg C

Best of luck CChris

 

[ShaunCorbs]

as a guide (& we work in Watts not BTUs now, have done for 30years)
15mm = 11000
22mm = 23000
28mm = 40000
35mm = 62000

Best of luck CChris

Unless your old school 😀 tbh I still work kw but converts for the boss as he only works in btus 😀

 

[CChris]

Several calls and emails from plumber and main contractor today.

Turns out some of the rads are oversized for asthetics as they took out some fairly large single panel rads from the 60s that stretched a window and have replaced with similar size but modern. Also he's removing five rads from the upstairs circuit and putting onto their own separate run to remove further loads from the upstairs circuit.

Also going to alter boiler pipework and sort out a bypass, fit all remaining rads etc.

Main contractor and plumber on site all day Monday and they have been tasked with demonstrating the system working as it should.

Can I book snow or at least a good frosty day for Monday please? 🙂

I may be light hearted about it, but seriously ripping the carpets and floors up to replace pipework in the future if it needs it seems just like trivial bit of upset after the build itself. We were supposed to be home end of November 2014 if that gives an indication of how farcical this process has been.