Sorry for being thick, but I can only find a small boiler in the kitchen and a hot water tank with another smaller tank above it which I presumed was the cold water feed (this is the one with the ballcock in it and has lots of water) in the cupboard. Thanks ever so much for your help...
I live in a flat with a small boiler and the hot water tank on about the same level separately. The system has two automatic air vents, one by the boiler and one next to the tank. The pilot light kept blowing out (due to overheating cut out) which the plumber said was due to an airlock. He...