Radiators warming when they shouldn't be

Discussion in 'Plumbers' Talk' started by PTFE, Apr 14, 2010.

  1. PTFE

    PTFE Member

    Hello all, wonder if anyone can shed any light on this one.
    I fitted a new boiler under the scrappage scheme into my dear old mum's:
    Open vented system
    Fully pumped
    One 2 port(normally closed) to isolate CH (i.e she can have HW or HW+CH but not CH only)
    Boiler (Vaillant 415) on ground floor of standard 3 bed semi

    There are 2 returns on the system. One from the coil and one from the CH. These used to tee together just above floor level before returning into the old floor mounted Glowworm Hide-Away.
    I mounted the Vaillant at wall cupboard height and moved the Tee to ceiling height to neaten the pipework up.

    Now the problem - when she had HW only selected the radiators begin to warm. I checked the zone valve and it appeared to be fine (ie still closed with the CH isolated), but changed it to one I had anyway so i knew there was no chance of it passing.

    But the problem was still there.
    It appears to me that when water from the coil return tees into the CH return, the heated water is going back into the CH system as well as returning into the boiler, therefore warming the rads from the wrong direction (she doesn't want or have TRVs fitted! :))

    I'm considering fitting a 22mm check valve on the CH return to prevent water passing the wrong way up it but I'm a bit concerned about the force needed to overcome the spring in the valve putting the system way out of balance (I suppose I could put a check valve on the DHW return too?)

    What do you think?
    Am I barking up the wrong tree?
    Could it be the position of the tee connecting the 2 returns being moved that has caused it?

    Thanks for any insight
     
  2. sounds like you are getting reverse circulation.
    there must be 1 tee only on the return between cylinder and boiler. its difficult to describe in words (easy with diagrams) if you do not understand how to configure a "Y" or "S" plan system. ask any heating engineer local to you they will show you. easy to fix. do not put any valves in system you will make matters worse !!!!!!!!
    Hope this helps
     
  3. PTFE

    PTFE Member

    Thanks for the reply 40 years.

    I do understand both S and Y plan mate, and the need for the Tee.
    What I'm a bit confused about is why it's only started happening after a simple boiler boiler swap. The only other thing I changed was the location of the tee - from 6" above floor level just before it entered into the old floor standing boiler - to 7' high just before it enters the new wall hung boiler.
    Nothing else has been changed.

    I've just uploaded a couple of diagrams of the system (they're in MS Word format). As you'll see it's basically just the height of the tee that's changed
    http://www.filefactory.com/file/b11a947/n/old.doc
    http://www.filefactory.com/file/b11a948/n/new.doc
    If yourself or anyone else could have a look I'd be grateful.

    And if it's an easy fix ... what is it?! ;)

    Thanks
     
  4. imran_

    imran_ New Member

    Next time get your Mum to have someone competent to fit it. Not being able to control HW independently is not only wasteful of energy but not compliant with Part L. One shudders to think how you commissioned the boiler correctly.....
     
  5. PTFE

    PTFE Member

    Next time get your Mum to have someone competent to fit it.
    That's a little unfair Imran. I am qualified to fit it, otherwise I wouldn't have done it.

    Not being able to control HW independently is not only wasteful of energy but not compliant with Part L.
    I know it is. That's why I'm trying to sort it out.

    One shudders to think how you commissioned the boiler correctly.....
    The boiler was commissioned as per MI. This is my mother's house ***!

    I didn't expect to have any problems following a straight swap. I've never fitted an open vented system from scratch. And whilst I'm aware of the importance of the placement of some of the components, I wasn't aware that the placement Tee on the 2 returns was crucial. I am however quite prepared to be put right on that if it is in fact the problem.

    So before I start re-piping to move the Tee I'm trying to seek the opinions of those more knowledgeable than myself - and having read your posts you are certainly one of them - as to the most likely cause of the reverse circulation.

    If you've had a look at the files I uploaded (or can get the gist of what I've done from what I've posted so far), can you - or anyone else - point to the problem please?

    Thanks in advance for any help/advice you or others can offer
     
  6. JP.

    JP. Screwfix Select

    What about whipping in a 22mm check valve (single) just before the T?..this will prevent back feed into the rad circuit.
     
  7. JP.

    JP. Screwfix Select

    To explain more fully. Fit the check valve on the CH return just before where the coil primary return is T'd into the CH return.
     
  8. PTFE

    PTFE Member

    What about whipping in a 22mm check valve (single) just before the T?..this will prevent back feed into the rad circuit.

    I mentioned that option was in my 1st post JP, although I was a bit worried about upsetting the balance of the system. And 40 years mentioned that he didn't think I should try it.

    It's still an option to try but I think even if it stopped the reverse circulation problem - which it would - it might cause the system to be so unbalanced that it wouldn't function properly.

    Thanks
     
  9. JP.

    JP. Screwfix Select

    Oh right yes you have indeed mentioned it and my apologies for not reading your post correctly PTFE. I had the problem of the CH warming up on HW only a long time back, and the fitting of the valve cured it.. I didn't notice any balancing problems etc and it worked fine. However that was what 15 or so years ago on a new system I installed..so things might be a bit different nowadays with respect to the fitting of a check valve etc. Good luck M8 anyway.
     
  10. PTFE

    PTFE Member

    Oh right yes you have indeed mentioned it and my apologies for not reading your post correctly PTFE.

    No problem, it was a long post mate!

    I had the problem of the CH warming up on HW only a long time back, and the fitting of the valve cured it.. I didn't notice any balancing problems etc and it worked fine. However that was what 15 or so years ago on a new system I installed..so things might be a bit different nowadays with respect to the fitting of a check valve etc. Good luck M8 anyway.


    This system was apparently fitted late 50s/early 60s.

    I suspect it might have been a gravity system originally as the primaries are 28mm but that might not be the case.

    I suppose putting a check valve on will do no harm in that if the system remains balanced then I'm sorted, but if it doesn't I could take it out again.

    But if anyone can shed any light on the root cause I'd be very grateful.

    Thanks for taking the time to answer
     
  11. YNWA

    YNWA New Member

    I think the problem was caused by moving the tee up from floor level to ceiling level. As the hot water is joining the tee for return you loosing some hot water into the heating circs, and by raising the t you may have helped this too happen.
    Sounds like you having one pipe circulation/ parasitic circulation, especially as you mention 28mm pipework.

    You need to read up on the three t rule
    read this http://danfoss-randall.co.uk/PCMPDF/Introducing%20Controls.pdf

    and scroll down to "getting the pipework right
     
  12. YNWA

    YNWA New Member

    Explain which way round the tee is ? I have a feeling that you have installed it like this....

    ................HEATING
    ....................!
    ....................!
    ....................!
    BOILER.-------!
    ....................!
    ....................!
    ....................!
    ....................!
    .................CYLINDER
    ignoring the full stops you get the picture
    If so then you have indeed promoted one pipe circulation.
     
  13. well explained YNWA I wanted to but could'nt think of a way without an essay LOL
     
  14. PTFE

    PTFE Member

    Thanks for taking the time to reply YNWA and 40 years.

    I'm pretty sure the 3 tees are ok relative to each other because I haven't acually moved or worked on them.
    The only tee I moved is the one joining the CH ret to the Cyl return.
    The old tee was just above floor level before entering the olf floor standing boiler.
    I moved it to ceiling height which is just above the new wall hung boiler.
    You can see the old layout [​IMG]here
    And the new one here
     
  15. PTFE

    PTFE Member

  16. YNWA

    YNWA New Member

    that tee is your problem.

    Hot water rises on the old layout the water would have had to be cold to enter the heating circs, instead it entered the boiler.

    But now you have gave the hot water a way out and to rise again before entering the boiler.

    Is it just your upstairs radiators that are warm ?
     
  17. PTFE

    PTFE Member

    You're right YNWA, I'm seeing that now as I look at my own diagrams! :)
    It's mainly the upstairs rads getting hot, the downstairs have a barely detectable rise.

    I'll go round at the weekend and do some adjustments and post back with the results

    Thanks
     
  18. PTFE

    PTFE Member

  19. YNWA

    YNWA New Member

    that looks more like it was before, so if it was ok before that may do the job.

    try and get an anti-gravity valve or low pressure check valve and stick that on your heating return.
     
  20. Still reckon its reverse circulation !! that tee most likely although its difficult to be 100% without a look
     

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