combi pressure


I’ve got a pretty new Heatline Vizo Condensing Combi Boiler. Everything was fine for the first couple of months and pressure held steady at 1.5 when cold, and rose to around 2 when the heating was on. Over the past few weeks, the water pressure drops below 0 turning the boiler off regularly. I can refill to 1.5 before going to bed, and it will be back below 0 in the morning. When I refill to 1.5 and have the heating on, the boiler pressure now rises to the maximum of 3. When the heating turns off, the pressure will drop again, eventually to below 0 within the space of maybe 8 or 9 hours. Whats going on? I cant find any obvious leaks (although the plumbing is underfloor), and there is no air in any of the rads. Ive drained and refilled the entire system a couple of times, but this has made no difference. Help! Its cold in the mornings and I cant afford a plumber!!


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    7 Responses to “Combi boiler pressure drops below 0 overnight and rises over 3 when on?”

    • Rebecca Slater says:

      Sounds like a fault with your pressure relief valve. this allows excess pressure to be relieved from the system and should be on the inlet side of the boiler, at least it is on mine, when you refill see at what pressure it lifts. If this is normal it may be the valve seat or the rubber. If not then you have a leak somewhere.

    • Madeline Whyte says:

      pump settings need changing

    • Theresa5 says:

      I would say you have got a leak somewhere.

    • Oscar Cooper says:

      Did you check the water temp? this should be adjustable and may be too low,

    • Laney Dutton says:

      probably the expansion vessel.theres a rubber bladder inside this has broken, you need it looked at by a corgi engineer, other wise you ll need a new press relief valve as well as expansion vess, take a look out side to see if the prv(pressure relief valve) is letting buy,you may see water dripping or running. easy to fix but expensive

    • Mateo Stone says:

      I agree, the bladder is either split or needs pressure again. The heated water has nowhere to expand to and is leaking from the relief valve.

    • Danna Nicholas says:

      sounds like your setting are wrong and it may have a 24 hour clock that needs adjusting

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