can a good plumber explain this

Discussion in 'Plumbers' Talk' started by chippyno, Nov 29, 2009.

  1. chippyno

    chippyno New Member

    potterton powermax 150ltr

    pressure dropping over 1 day

    all pipes are in the ceiling space between upstairs and downstairs , no leaks are obvious.

    replaced expansion vessel.

    checked flexi hose to primary expansion vessel in the boiler.

    replaced prv.

    any ideas of the cause , when boiler on with ufh and rads pressure often between 1.5 - 3 bar

    prv works at about 3.2bar , but it dont get to this , ive manually added more pressure to check.

    I am pretty handy at most things , but am lost at this

    any help most welcome.:):);)
     
  2. poolcorgi

    poolcorgi New Member

    expansion vessel is undersized for the system
     
  3. musky1

    musky1 New Member

    Wrong,if the pressure vessel is undersized the pressure would increase and eject it out of the PRV.
     
  4. chippyno

    chippyno New Member

    the pressure vessel is the one that come with the bolier , Ive replaced it of exactly the same size...
     
  5. poolcorgi

    poolcorgi New Member

    any ideas of the cause , when boiler on with ufh and rads pressure often between 1.5 - 3 bar =======

    if its rising that amount the ex v is undersized

    and if the leak is not obvious the boiler is a good place to start looking
     
  6. Captain Leaky

    Captain Leaky New Member

    I agree. Either undiscovered leaks or undersized exp v.
     
  7. joinerjohn

    joinerjohn New Member

    I had a leak on my combi once. Twas the compression joint where the ch pipes came out of the boiler. Leak was so slow that the leak was evaporating as it leaked. Only found it when the ch had been off during the summer months (week).
     
  8. musky1

    musky1 New Member

    v.

    Carnt believe you Leaky,its a like for like exp vessel,if its under sized the pressure will increase. Its got fuckall to do with a pressure drop. That is a leak. ***
     
  9. G Brown

    G Brown New Member

    It is most likely a leak...or a dodgy EXP V
     
  10. Teuchter

    Teuchter New Member

    Shooorly an undersized expansion vessel will allow the pressure to increase to where excess stuff is ejected via the PRV - so when the system cools down again - voilĂ  - low pressure?

    Place a container under the PRV discharge pipe and see if anything comes oot.
     
  11. tomplum

    tomplum Active Member

    you mentioned ufh, a leak in there would't show for a long time,
     
  12. chippyno

    chippyno New Member

    there is no prv leak .

    but it seems to be that when the rad circuit is on the pressure rises to just under 3 bar then when the rads curcit goes off it drops to just under 1 bar then it drops gradually then it locks out.

    how long would it take for a leak to show on a pb ceiling ?

    all rads hot top to bottom ....im lost
     
  13. Captain Leaky

    Captain Leaky New Member

  14. Did you check your new expansion vessel for a charge?
     
  15. imran_

    imran_ New Member

    Dear OP,


    You change various parts, without reason but a good guess
    You never say you check/test the parts
    Repeat steps above, presumably charging each time.

    Cowwwwwwwwwwwwwww-boyyyyyyyyyyyyyyy.

    It's quite obvious that if the pressure increases to "just under" 3 bar - a standard for sealed central heating systems, that there's a PRV pi$$in somewhere. At an outside chance there is a leak under pressure but unlikely.

    Sounds like an undersized exp vesssel and water out of the PRV. Who cares if you've replaced the original like for like. Does that mean it's the correct size.

    Next time pretend you're a DIYer rather than a cowboy/thief. We might take pity on you.
     
  16. Teuchter

    Teuchter New Member

    He says there's nothing coming out the PRV.
     
  17. smithp60

    smithp60 New Member

    Ouch, (Imran), quite a volley there.

    From the symptoms described I would say there is a definite leak and it will be on a rad valve!

    You need to take off the plastic caps and inspect all rads on full burn. The water can be leaking and evaporating before you find it coming through your ceiling.
     
  18. tetleyman

    tetleyman New Member

    Have you checked the auto air vent it is on top of boiler right hand side has a plastic cap on top of it but this should be slackend off but if this is passing it could be your problem
     
  19. doing a bit

    doing a bit New Member

    what pressure are you putting in the system when its cold ? try dropping the water pressure and checking the exp vessel pressure , should be around 10psi , then repressure
     
  20. joinerjohn

    joinerjohn New Member

    Imran says "Sounds like an undersized exp vesssel and water out of the PRV. Who cares if you've replaced the original like for like. Does that mean it's the correct size.
    " So the manufacturer has undersized the exp vessel? I don't think so matey. unless you know different?????
     

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