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 managed to force the air out of the system, but since then it's been getting worse again. The air vent by the boiler was letting out more and more air when we relit the pilot light each morning before it started heating properly. I found one radiator was cold at the top so tried to bleed it but didn't turn the heating off first (stupid!) so it sucked more into the system. Since then it has done nothing but blow lots of air out of the vent when we relight it, before going out. I thought this would eventually fix the problem by getting the air out of the system but it is getting worse if anything and I am worried about heating a dry boiler if it is just full of air. The radiators have no air in and there is no flow getting round to them and no air came out of the pump when I tried the bleed valve there, just a tiny trickle of water. We have the plumber coming again on Monday, but in the meantime is there anything at all that I can do to get any more air out of the system? Is there anything other than a lot of air that could be causing these symptoms (I suspect we have that black gunk that is mentioned a lot, but I can leave that for the plumber to deal with). Thanks for your help.