When my boiler is supplying the central heating and you draw hot water the pressure jumps up by about 0.5bar and then drops back down to it's normal 1.5bar when you close the tap. It works fine but I would expect the two systems to be separate and not to affect each other. Is this normal. I also have a slight leak in the central heating system as the pressure drops by about 0.5bar per week. I am going to try some leak sealer next but anyone have any ideas on what else it maybe?

gary, December 2007

Hi John,

Thanks for that. I checked the pressure vessel and it was empty (well atomospheric pressure) so I pumped it up to 0.8bar and it's fine now - the needle hardly moves when you draw hot water. The leak turned out to be muck or something in the pressure relief valve. I blasted it through with hot water from the heating system and it has sealed itself. I had visions of a new boiler but it cost me nothing in the end and gave me something to do on boxing day.

gary, December 2007

This doesn't sound too unusual but you should check that the pressure vessel inside the boiler actually has air in it...they are topped up by a bike pump with a normal Schrader fitting. Your leak could be anywhere - in the pipe work itself or in the boiler heat exchanger if there is no obvious problem.

John, December 2007