CH boiler loses lots of water

[Peter Weilbacher]

Hi again,

since some time, our central heating boiler (an older Vokera) loses a lot of water every day. It seems to drop (sometimes even flow) from the pipe that leads to the outside of the house. This only happens when the heating itself is turned off, so that the boiler is in "hot water" or "off" mode. This is most notably over night, when it is switched off. In the morning, the pressure on the meter at the boiler is around 2.5 bar (I would guess due to the heating by the pilot light). When I switch it on, it gurgles and the pressure quickly drops to around 0.1 to 0.3 bar. Sometimes, when it is switched off, I can also hear what I would describe as sigh from the boiler.

Can someone tell me from these observations what could be wrong with it? Is it some kind of safety valve that is broken? Is it easily fixable? Or do I have to drain the whole system? Then I would better call someone in, but not before someone here explains what that guy will likely do...

[Ed Sirett]

[Peter Weilbacher]

Of course, stupid me, not to look in the FAQ first.

Unfortunately, touching the red knob mentioned there was a bad idea, now the system does not even keep pressure for 5 minutes any more... Guess I better call someone.

[Hugh]

sounds like either a replacement pressure relief valve needed, or expansion vessel - when the diaphragm goes, you get wildly fluctuating pressure - simple and straightforward to replace. Hugh (novice CH fitter who hasn't blown anybody up yet - but I'm working on it)