Hi, I have a microbore system with Potterton Gas Heating - It is conventinal setup with tanks and immersion tank. Recently the system has starting banging loudly so I checked for air locks. What I mistook for the 'hiss' of the radiators being bled was in fact the 'Hiss' of them emptying! It is apparent that the system isn't filling. The expansion tank valves etc work OK but level high due to discharge from pipe. The pump (set on highest speed) and motor valve (On Auto) appear to be OK. The knocking turns out to be steam from the expansion pipe, not air as I thought. Any Ideas?? Thanks
