My combi boiler loses pressure overnight,on further inspection i found that when the boiler fires it loses water out of the flue (not the overflow!) can anyone tell me why?
Thanks
A product of burning gas is water vapour - you wont be losing pressure thorugh the flue - if you were the whole boiler chamber would be full of water and wouldn't work at all.
Check system for leaks, check PRV and check to see if pressure rises alot when the heating is in use.
Boiler pressure drops when in use gradually over a period of 2-3hrs every time the boiler fires a sposh of water comes out of the flue and there seems to be double the amount of steam coming out.
There is also a damp burning smell coming from the boiler!
