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Combi losing pressure

Discussion in 'Plumbing and Central Heating' started by dal5band, 23 Dec 2014.

  1. dal5band

    dal5band

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    Boiler model Vaillant Turbomax - 837 E approx. 10 years old.

    My mum's boiler was running fine until I noticed one of the radiators had air in it and I bled it. I had to top up the water to bring the pressure up to normal. Now, it keeps losing pressure over a few days. I can't see any obvious leaks anywhere - but there is a drip on the pressure relief pipe outside. Seems by topping it up I triggered something.

    Just want people's opinion - would it be the relief valve or the pressure vessel ? It's under maintenance - I want to be prepared to argue the toss when I call the engineer next week.

    Thanks in advance
     
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  3. Dan Robinson

    Dan Robinson

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    Could be either or both.


    Easy to check.

    The bleeding of the rad was more likely a consequence of the failure rather than the cause.


    Just don't say anything to the company about bleeding.
     
  4. StevieV1

    StevieV1

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    Several possible causes. I had this issue several years ago and tracked it down to the diverter valve - It was letting some of the CH water through the DHW side so pressure was dropping - resolved by changing the diverter valve.
     
  5. Bunnyman

    Bunnyman

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    That's the biggest load of ****** I've ever heard? If the diverter was passing it won't affect pressure in any way, an if it did the pressure would rise not drop as mains pressure is always higher than heating pressure lol
     
  6. StevieV1

    StevieV1

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    So if water was leaking from the sealed CH side into DHW side and was not replaced via the filling loop, the pressure wouldn't go down? Got news for you, it did on mine. OP was asking for possible reasons for his pressure drop, I provided one that happened to me. But you obviously know better so....

    Try reading my post properly
     
  7. dal5band

    dal5band

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    UPDATE : It seems it's holding steady at just 1/4 bar - just in the green zone and the boiler is still working so I am leaving it alone. It's the topping up that caused the relief valve to drip - will get it fixed at a more convenient time.

    Original Poster
     
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  9. Bunnyman

    Bunnyman

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    Sorry stevie u obviously dont understand systems or grasp the physics of it :)
    If mains pressure is 1 bar plus ( which is the legal minimum) if there is any crossover from heating to mains it cannont physicaaly go below 1 bar can it, someone bin pulling ur leg
     
  10. ALCPlumbing

    ALCPlumbing

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    I thought the minimum was half a bar. Irrelevant and unimportant but just wanted to check.
     
  11. sooey

    sooey

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    Sounds like the pressure vessel wants topping up, the rad with air in it was acting as a vessel till you bled it.
     
  12. dal5band

    dal5band

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    Ahh !! Sooey, what does topping up the pressure vessel involve ?
     
  13. denso13

    denso13

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