Worchester Greenstar 15i MK111 Pressure loss

Discussion in 'Getting Started FAQ' started by Robert Stroud, Nov 7, 2018.

  1. Robert Stroud

    Robert Stroud New Member

    If anybody could help?

    I have a Worchester Condensing Boiler that loses pressure every day, I have recently had some electrical and hot water plumbing work done for a new kitchen, with upstairs floorboards coming up to run a new electrical cable for an Oven and rerun hot water pipe for the new location of the sink.
    I lose pressure everyday, filling to 1.5 bar, when heating is called it raises to over 3 bar with pressure relief letting water out, but stops when under 3 bar and then cools to 0 bar.
    If I run the boiler just to heat water cylinder, it holds and maintains pressure.
    I have bled all radiators, for no air to be released and tightened all valves and fittings.
    So after reading other forums I have come to the conclusion it is not the pressure relief valve or the expansion vessel?
    Would I be correct?
    My next idea is to close all Radiators and run the boiler in the hope I might find offending leak to a certain Radiator and not have to open all the floorboards upstairs, is this a good plan?
    Thanks in advance.
  2. Mike83

    Mike83 Well-Known Member

    The vessel needs charged.
    The prv closes as the pressure drops back to under 3 bar.
    Then once the system cools the volume of water contracts ending up at zero pressure.

    When using only hot water the volume of water being heated is far less than for heating.
  3. joinerjohn1

    joinerjohn1 Screwfix Select

    Once the prv has opened, it’s possible it’s not closing all the way ( crud preventing the rubber washer sealing fully) Water pressure would then reduce overnight to zero. Could also be, as Mike suggests, the pressure vessel needs recharging. I’d look at these two possibilities before lifting floorboards looking for a leak.
  4. Robert Stroud

    Robert Stroud New Member

    Thank you both for the replies, prv is pressure release valve and pressure vessel is expansion vessel?
    You have saved me a lot of time and effort, was worried before calling out someone.
    Thanks again.
  5. Mike83

    Mike83 Well-Known Member

    Do you know how to charge the vessel correctly.
    The vessel will be full of water and all this water will need pumped out.
    It will be easier if there’s access to a drain.
  6. Robert Stroud

    Robert Stroud New Member

    No I do not know how to charge the vessel, I don't even know where it is! I believe there is a boiler drain off either near the boiler or on pipework by emersion tank
    I did read on another forum that I could do a temporary fix by letting air into one radiator to act as the vessel.

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