vaillant combi boiler

[heinrich]

I have a VCW-GB 242 EH on my heating system. I loose approx 1 bar per day in my heating. I want to test if it is a leak in my system or an internal problem on the boiler. I have no obvious external leakages. Can anyone advise an easy test?

[gucciman]

fill the boiler up to 1.2 bar when the boiler is off and cold. run the boiler on heating at full blast and keep an eye on the pressure guage, if it goes up to over 3 bar and then the pressure relief valve opens up and dumps the water outside then you have a problem wth your expansion vessel.
if the above doesn't occur but your still losing pressure then you have a leak on your system somewhere, if your losing that much water i would expect to see wet patches somewhere so go round all your radiator valves looking for leaks and see if theres any water around the boiler anywhere.
my money would be on theexpansion vessel needing re-pressurising