Your boiler has detected a potential safety issue where the gas valve is not closing properly or the control board is misreading the gas flow.

Gas valve shutoff delay | Gas valve leaking, electronics defective

What causes this fault?

This fault occurs when the boiler's control board detects that gas is still present even after it has commanded the gas valve to close. The most common cause is a physical internal leak in the gas valve itself or a communication error on the main circuit board that prevents it from shutting off the fuel supply correctly.