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Combi boiler needs pressurising almost every day.

Discussion in 'Plumbing and Central Heating' started by judder, 22 Apr 2013.

  1. judder

    judder

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    I have a 5-year-old Worcester Bosch boiler which I have to re-pressurise almost every day. I have two questions:
    1) why does the pressure drop - where does the water go?
    2) have you any idea what might be wrong with my boiler that its pressure drops so often?

    Thanks in advance.
     
  2. Jamesie

    Jamesie

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    Have you got a pipe that comes from the boiler and goes outside(copper) if so is there a puddle below? If so you pressure relief valve may have debris stuck in it, or its knackered.
    If above ok, check all your rad connections, make sure you have no leaks.
     
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  4. bolshy

    bolshy

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    Does the pressure rise to 3 bar when heating is on? Have you ever had it serviced, and expansion vessel charge checked?
     
  5. MANDATE

    MANDATE

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    Basically water is being lost. there may be a small leak in the system or most likely the pressure relief valve is opening when the pressure reaches 3 bar which is what it is supposed to do and this will reduce the pressure to almost zero.
    The time it takes for the pressure to drop will be a strong indicator.
    The expansion vessel is supposed to contain 'air' which can be compressed when the heating is on and the water expands in volume, the extra volume going into the vessel.
    The air in the vessel should be initially pressurised to approx 0.8bar.
    Too high a pressure means too much resistance so the water takes the easier route out through the PRV.
    Too low a pressure means that when water is put into the system it fills or partially fills the vessel, so very little air to compress so when it expands there is nowhere for it to go only out through the PRV.
    Unfortunately PRVs once opened may not seal correctly due to dirt so it would need cleaning or the easier option replace it with a new one.
    So first action would be to check the vessel and correct it if at fault.
    Observe the rise in pressure when heating is on. It should only rise about 1bar and if it approaches the 3 bar mark then the vessel has not been corrected properly. Note there are two requirements when charging the vessel with air (a) the correct pressure and (b) ensuring the vessel does not contain any water, water pressure must be zero (water side open to atmosphere.
    If pressure is lost gradually when heating is not on then suspect the PRV not being fully closed or a leak elsewhere in the system
     
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  7. oilboffin

    oilboffin

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    Take the top off the valve on the expansion vessel depress the schrader valve pin and if water comes out the vessel has gone fit new one and all should be well
     
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