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?