I'm thinking of closing the stop cock and opening a basin tap to depressureise the mains coming in then and running the boiler (at a normal starting pressure). That would rule out water coming in through the mains side.
Hi All, I recently had an issue where the boiler turned off due to low pressure in the CH circuit. I have since found that the pressure vessel diaphragm had failed so I put in a new one and pressurised the air side to 1 bar. This has not fixed the issue. When the boiler is heating it will go up...