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Reverse Circulation? (threads merged)

Discussion in 'Plumbing and Central Heating' started by blackbirdxx, 24 Dec 2020.

  1. blackbirdxx

    blackbirdxx

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    Hi,
    I had a totally new S-Plan unvented CH system installed last year with new boiler, rads etc and now have a longstanding problem of upstairs rads getting warm when the HW is on/CH off. Apart from this, he has done a very neat job.
    My view is that it's poor pipework configuration and I have reverse circulation with hot water entering the return pipe. I'm sure that the plumber knows but basically just wants me to go away as any fix will be time and money. I appreciate that any rectifications will include reopening the system and possibly damaging a totally redecorated house. I could of course have a non return valve installed, or alternatively, just turn the rads off during the summer months. Its damage limitations I'm thinking of.
    If you were in my situation, what would you folks advise as the best option??
    Many thanks in advance...
     
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  3. oldbuffer

    oldbuffer

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    1. Its essential that the return from the hot water cylinder primary coil is the last connection on the system return before the boiler.
    2. The installer should know this.
    3. If it makes the connection difficult, he / she should:
    3a. Price accordingly.
    3b. If not apparent when surveying the job, make the problem known as an extra during installation.
    4. I can't see any reasonable excuse for not doing it properly in the first place.
    5. The installer should, in my opinion, fix it for no additional charge as its such a fundamental point.
    6. With regard to damage limitation:
    6a. A non-return valve would probably do the trick. But make sure its accessible, and anyone working on the system knows it is there. Otherwise it can cause strange effects (e.g if power flushing).
    6b. If the valves are all TRVs, shouldn't be a problem turning them off. If they are ordinary wheel head valves, these often start to weep from the gland seals if used on a regular basis.
     
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  4. blackbirdxx

    blackbirdxx

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    Thanks for the response,
    Strangely, the plumber has said that it has been installed according to the 3-tee rule. Unfortunately, I can't confirm this as the pipe connections are hidden. If the connections to the return pipe are in the correct order as he says, is it reasonable that he does all of this extra work or is it just an unlucky outcome to the installation. It is an old house so he possibly was restricted to where he could route pipes. That said, is the NRV option the best option and an accepted solution or is it a bit of a bodge? I do have TRV's on all the rads so could turn them off in the summer if its only going to create probs in the future.
     
  5. blackbirdxx

    blackbirdxx

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    Just to clarify, when you say 'the return from the hot water cylinder primary coil is the last connection on the system return before the boiler' you mean closest connection to the boiler on the return pipe - yes?
     
  6. iateyoubutler

    iateyoubutler

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    I had this problem with my system, and when I took the floor up to investigate I found that the bathroom radiator was the culprit - it was plumbed between the cylinder return and the boiler. The hot water backed up through that one radiator and then into all of my upstairs radiators giving me the exact same trouble, it was annoying to say the least! In the end I actually cut off and capped the original cylinder return pipe and ran a new one directly back to the boiler, problem solved - all radiators cold when hot water was on
     
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  7. ianmcd

    ianmcd

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    Yes all rads must share the same return, the HW return MUST be the last connection to the return circuit
     
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  8. footprints

    footprints

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    This may help clarify what goes wrong.
     

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  9. blackbirdxx

    blackbirdxx

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    Should there be a minimum length of return pipe between the cylinder return T and the radiator return T to prevent reverse circulation?
     
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  11. iateyoubutler

    iateyoubutler

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    I don`t know if there is a set recommended length, but if I remember rightly on my system the cylinder return is about 6ft downstream of the last radiator, and the 2 returns tee together about 300mm from the boiler
     
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  12. blackbirdxx

    blackbirdxx

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    I only ask as both the radiator return and cylinder return pipes connect to the main return pipe within the ceiling void between ground and first floors. This must mean that both connections must be very close together. Is this OK?
     
  13. blackbirdxx

    blackbirdxx

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    After further investigation , I notice that the rad in the upstairs bathroom may possibly be the problem causing this reverse circulation. This radiator is set up to work off the hot water and not the central heating which is not unusual. The return pipe from this radiator raises from beneath the floor boards by about 400mm in the upstairs airing cupboard and then descends to connect into the return pipe coming out of the cylinder. As this return pipe from the bathroom and cylinder is now the last T before the boiler, will this be a problem as its now effectively a radiator return?

    Anyway, Merry Xmas to you all. Thanks for your ongoing help.
     
  14. ianmcd

    ianmcd

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    yep that is your problem
     
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  15. blackbirdxx

    blackbirdxx

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    Aah, thats great to know. For information, when you have a bathroom rad fed from the HW supply where do you normally connect up the rad return pipe to??
     
  16. ianmcd

    ianmcd

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    sorry I mis read your post, if the bathroom rad has a flow and return from the flow and return from the HW indirect circuit then that is not your problem, that was quite common in older houses as a heat dump for solid fuel boilers
     
    Last edited: 25 Dec 2020
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  17. Pin 5

    Pin 5

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    Put some pics up of the install.
     
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