vaillant boiler slowly loses pressure

Discussion in 'Plumbers' Talk' started by Sukhvinder, Jan 28, 2016.

  1. Sukhvinder

    Sukhvinder New Member

    Hi all, so my parents have had their valiant boiler for about 7 or 8 years and it's never let us down. Recently it's been losing pressure and flashes a F28 error.

    So after some time I've figured out the below pattern where it only happens when the central heating is on and days it's not used the pressure stays fine.

    So I watched the pressure gauge and it's on 1.5 bar for example with the heating on, when someone turns the hot water on the boilers sound changes straight away as it gives hot water. When the hot water is turned off there is a pause of about 10 seconds and a buzzing sound (a divertor valve maybe from my basic understanding) and the pilot re ignites and it sounds like the heating is pumping round after the pause.
    But the pressure on the gauge is slightly lower than the 1.5 it was before the hot water was turned on.

    This can happen about 7 or 8 times and the pressure gets so low that the F28 error shows and the error lights are flashing.
    When looking outside the boiler is throwing out water from the overflow pipe.

    I hope the above is enough information for someone to know what I'm talking about. Thanks for reading!!
     
  2. Hi Suk.

    What's your 'overflow pipe'? Is it a 15mm copper pipe pointing down to the ground, or is it 22mm plastic and aiming in to a drain?

    If the former, then it's the safety discharge pipe and this only releases system water as a safety feature when the pressure reaches around 3 bar (that's high...). Mind you, it can also trickle when it's faulty, but yours doesn't seem to do this - only gives a glug at these specific moments?

    What type of pressure gauge do you have - is it digital or analogue? If analogue then you should be able to observe what the pressure does during this process.

    I'm guessing that when you turn off the hot tap and you hear that buzzing sound, the pressure shoots up to 3 bar - and releases that water.

    If it's digital, then they often switch display when DHW is being drawn (mine does at least...)

    Anyhoo, please (a) confirm what pipe it is you are talking about, and (b) try and note when the water comes out. If you can see what the pressure is doing at that point, then great.
     

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