D
diamondgas
Less likely to be the gas valve, more likely one of the boards depending on how your boiler is set up. The thermostat should interrupt the power supply to the gas valve when shut off. What your describing seems to indicate that this is not happening. Possibly a fused relay on the board, but that's a guess! You'll need to get someone familiar with your boiler, it's a commercial appliance, to trace the cause.
