Combi-boiler: Pressure loss

[Plumb tart]

pressure relief valve shouldnt be dripping give it a couple of spurts and see if it closes tight again

Thanks Newbie1 for mentioning " a couple of spurts" you have just solved a different problem I was having ...your a star 😎 cheers

 

[LIFES A GAS]

Not sure you have cured the problem, if the PRV was dripping all the time then you still would be losing pressure when operating water only. I would think the problem is caused by the expansion vessel, is the pressure rising on the gauge when the heating has been running some time? if it is and reaches 3 bars then the PRV will automatically open to release the excess pressure, this does not normally happen when running hot water even if the expansion vessel is not doing its job as the system water temp does not keep rising as it is transferred to the hot water via the water to water heat exchanger.
Hopes this helps Martin