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I have a LCG Combi boiler that is suffering pressure loss. It loses pressure both when running c/heating and when running hot water mode only. Lately it loses about 0.5 bar every couple of days requiring top-up. No sign of water leak internally so if pipes leak, they must be under house. If pressure drops when running in alternative modes (i.e. supplying different pipes) isn't it more likely to be boiler problem? But we have had annual maintenance check which showed no problem with boiler and have had liquid sealant put into c/heating system without any affect. Any clues or advice appreciated. We have parquet and wood floors everywhere so reluctant to randomly rip up flooring until absolutely necessary.

It does sound like a leak somewhere in the system as its only losing up to 0.5bar at a time.If it lost all its pressure it would probably be the expansion vessel which had lost its charge.Check outside where the pressure relief pipe comes ouy of the wall and see if its dripping water.If it has ,this then leads to the expansion vessel fault or pressure relief valve fault

hi, just looking around for help with our boiler losing pressure.

has been ok, but has gone back to losing pressure all the time again, basically can't have on over night as the fault light will just be lit in the morning, checked rads all heat fine, no signs of leaking from what i can see...

had a look outside and the pipe that comes out seems to be, well, the area below the pipe seems damp as if water has been coming out but as i know nothing about plumbing dont know what to do. heard someone mention something about this pipe outisde when looking around for help previously, could this be the problem?