My Worcester Heatslave 20/25 oil fired combi boiler loses pressure over a few days / week or so. It heats two one bedroom holiday cottages and my office.
This is a long standing fault - the chap who maintains it has looked at it several times to try and cure the fault - he has changed the expansion vessel, and as far as I can tell there is no weep from the safety valve or any sign of water / water stains within the boiler itself. We came to the conclusion that there must be a weep in a pipe under the cottage floors, but no, we've just refurbished them and replaced the floors, and examined the pipework - absolutely no sign or evidence of leaking. The flow and return pipes to my office have isolation ball valves at the boiler, and the pressure still seems to drop when they are isolated. Other than the auto air vent where else could it be leaking?
I am assuming that if there was a heat exchanger leak, the pressure would increase rather than fall, as mains pressure leaks into the system - is this correct?
AWEM