water level rose in CH expansion tank with system off and resolved when

[ignored]

I've just got back from hols to find the CH expansion warning pipe dripping and algal?sp growth on the lean-to roof as a result so it had obviously been dripping for some time. The boiler had been off while we were away. I decided to leave investigating until today but magically the dripping has stopped now that the boiler has been run a few times for hot water. Why'd that happen?

[BillR]

The ball-c*ck has been exercised and the washer is sealing better?

Worse case is your pimary coil in your hw cylinder has a small leak and this is normally not noticed when you're drawing off hot water.

[ignored]

Ok thanks Bill, I'll bear those in mind