Constantly losing pressure means a water leak somewhere...either within the boiler itself, the system pipework and radiators, or to the outside via a leaking pressure release valve. The expansion vessel, if faulty, will eventually fill up with water anyway - maybe its leaking itself? They are really there to keep the water pressure constant and they can be fitted externally from the boiler.
John
May 2009
howtomendit.com for free repair help, information and advice.
