Originally Posted by BanziBarn
Question: should the gauge be showing running pressure or 'boiler off' pressure? I.e - should I charge the boiler up so that it shows 2 bars when it's not running?
I'm pretty sure the the rads were installed with the boiler about 15 years ago.
Banzi,you need to refill the system when it's cold
Filling when the system is running is not recommended,as the water in the system is already hot,therefore expansion will have already taken place,and any reading you get from the pressure gauge will not be accurate.
My Combi's instructions state a pressure of 1.5bar when cold and off.
I would have thought that were there leaks within the system,at 15 odd yrs of age,the leaks would have shown up by now.
A fairly reliable way of finding out if it is the expansion vessel causing the problem,is to locate the discharge pipe.
It should be located near the flue pipe,which comes out of the external wall,normally
behind the boiler,the discharge pipe is a 15mm pipe and looks like a overflow pipe on a toilet.
If you find the discharge pipe,tie a see through plastic pipe over it,but DON'T make it air tight.
If the bag collects water,it's because the system is overheating,and because the expansion vessel has lost all it's pressure the membrane within can't expand, so the heated water will get kicked out through the pipe,and go in the bag.
If water gathers within the bag,that's the water that has escaped the system,that has resulted in your pressure loss.
PS,I'm not a plumber,nor heating engineer,but I have had Combi's since they first came on the market,and I've had my fair share of problems with them, and where possible,I like to fix them.