Hi, Check all rad valves for leaks, but it could also be a sympton of a leaking pressure relief valve. You will need to locate the PRV pipe (15mm copper, always outside, usually near the boiler) you can tape a freezer bag to it. This will show you if it is passing water. Top up pressure and check daily. If not either of these, probable expansion vessel loss of pressure. You will need to call someone, but at least you will have an idea of the problem..Good luck.
Mike, February 2010
