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DHW heating radiator


graham1

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Installer has just fitted a new 3 way valve but still the same problem - when DHW is on 2 radiators heat up to much hotter than when heating is running. This is a new installation not yet signed off. Is there any other cause for this except faulty valve?

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Radiators are on ground floor.

It is a completely new installation. including piping and radiators. Has had problem since start and installer changed valve motor.

 

Not sure if this is the way to respond messages - if not can you direct me in the right way?

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On 17/01/2022 at 07:51, graham1 said:

2 radiators heat up to much hotter than when heating is running

 

Probably fitted with TRV's - is pipe going into the TRV hotter or cooler than the other side when radiators shouldn't be on (trying to figure out flow direction) 

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Like PeterW, I'm thinking it might be that the return path from DHW coil is finding it easier to go via a couple of radiators & their returns back to the boiler than the intended path. This could show up as one of the radiators having a hotter return pipe than its feed.

 

I can't be arsed to draw a picture but in words: the DHW return meets a radiator return where they're both on their way back to boiler. This rad would be the one with a hotter return than feed. Its feed connects to the same feed as another radiator, which has a less restrictive return to the boiler. This circuit is then hot when it shouldn't be.

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When the heating is off I am willing to bet it is the return pipe getting hot first on the radiator.

 

Ask the installer he piped it with a common return.  That is the work of the devil and should be avoided, always fit a separate return for radiators and hot water.

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4 hours ago, graham1 said:

I had a message from the installer saying it is a naturally thing that radiators closest to the 3 way valve should get hot even tho the heating is off

He's talking out of his arse.

I've fitted new heating systems ( and fixed older ones too ) for north of 25 years, and what he says is a crock of crap. I've converted 50 year old systems from gravity hot + pumped heating, with pipework that looks like a rat-run with T's here there and everywhere, to new sealed and pressurised S & Y-plan and I've never had this issue.

If the 3 way valve has been installed correctly, and more importantly WIRED correctly, then zero heat should get to any of the radiators.

2 hours ago, ReedRichards said:

A non-return ("check") valve would presumably solve the problem.

That would only be applicable if it were a gravity DHW scenario where the heating would get reverse convection flow to rads higher than the heat source.

@graham1 The quickest way to solve this would be at ask your installer to put a gate valve in the flow to the rads, between the zone valve and the first rad, and then to close it. If the issue remains, further investigation into the plumbing layout is needed. Is this a 100% new install or a retro-fit new boiler onto existing pipework and rads?  

Edited by Nickfromwales
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21 minutes ago, graham1 said:

This is a completely new installation of an ASHP radiators & pipes.  Is it possible that wiring could be wrong?

 

On 17/01/2022 at 07:51, graham1 said:

when DHW is on 2 radiators heat up to much hotter than when heating is running

OK. With an ASHP there is a 3 way DIVERTER valve, and with a traditional heating ( aka S-plan or Y-plan ) there would either be a 3 way MID POSITION valve. The diverter will ONLY allow heating OR hot water, eg never the two together, as with an ASHP there are pre-set temp changes per the duty ( say 40oC when diverter is flowing to heating and then 55oC for hot water etc ) so if I read the above correctly there is still flow going to the rads when heating is selected, and the rads gets hotter during hot water 'mode', and this is a brand new sealed and pressurised system? That tells me that the 3 way valve is either plumbed in incorrectly, or "passing". The 3 way valve has deffo been replaced and you witnessed that happening in person?  

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My radiator pipes are split into two zones.  The return water from the small zone can either go down the return pipe or backwards through another radiator on the large zone.  I can see no reason why it should want to do the latter but it does; when the large zone is off this radiator still gets hot.  Rather than trying to figure out why (nothing obvious) I thought it would be easiest to fit a non-return valve to prevent it.  

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Hi NIck etc.

It is a brand spanking new pressurised ASHP system. Only only one zone.

When heating is on all radiators function normally.

When DHW is on the heating closes and after a while, about 20 minutes 2 radiators heat up to around 40`.(It looks as if the 2 radiators are linked ) None of the other radiators do anything until DHW turns off.

A new motorised part of the 3 way valve was replaced and being nosy as I am I saw it happen:)

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On 22/01/2022 at 09:12, ReedRichards said:

I take it you don't know and cannot see how the pipes have been routed?

I see today that the 3 way valve has heating / cylinders  installed to ports B/A instead  of A/B. as instructions state would this have any effect?

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  • 2 weeks later...

You would get central heating when the DHW cylinder was calling for heat and your water would be heated when the room thermostat was calling for heat.  But that is only if the wiring was  "right" and the 3-way valve was "wrong".  So long as the wiring matches the valve orientation I don't see that it matters which way round it is.  

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  • 2 weeks later...

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