I have plugged all the leaks I can find and taken the boiler up to its working pressure and beyond. The safety valve operates at about 10% over the 'red line' and is able to keep the pressure down while the burner works at full blast.
I could not check the pressure control switch as I had to use domestic mains to power the burner; the inverter supplied could not provide the current drawn by the burner. In trying to get it working, I have applied a carbon conductive grease to the battery terminals.
