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Leak from PRV only when boiler is firing

Discussion in 'Plumbing and Central Heating' started by pdaj0463, 20 Dec 2020.

  1. pdaj0463

    pdaj0463

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    I have a Vitodens 222F boiler and it leaks from the PRV, not all the time, but only when the boiler is firing.

    My first attempt to fix this was to replace the PRV, which I have done twice now. This has not helped. I have also tested the PRVs that I removed and they don't leak when connected directly to the mains.

    My next thought was that mixer taps were perhaps leaking from cold to hot at a pressure higher than 3 bar. To rule this out I fitted a pressure reducing valve after the mains stopcock and set it first to 3 bar and then to 2.5 bar. This did not help either.

    Finally I added an extra expansion vessel to be certain that there was enough expansion capacity (I do have 100m2 of UFH). I also checked that the expansion vessels in the boiler for CH and DHW were charged correctly. Again this didn't help.

    When the boiler fires and the PRV leaks, it is not a huge amount, just a slow drip. When this is happening the CH pressure dial on the boiler is showing about 1.5 bar.

    Does anyone have any idea what might be going wrong?
     
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  3. Madrab

    Madrab

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    Have you checked that the gauge is reading correctly? It does point towards the pressure in the CH system is lifting the valve when it's heating up/hot/expanding.
     
  4. pdaj0463

    pdaj0463

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    Thanks, I will check that and post back.
     
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