Your boiler is still detecting a flame even after it should have turned off, which is a safety concern that prevents the system from running.

Flame detected after gas shut off.

What causes this fault?

This fault occurs when the boiler's internal sensors continue to detect heat or an electrical signal from a flame even after the gas supply should have been cut. The most common reason is a gas valve that hasn't closed properly or a faulty sensing probe that is sending an incorrect 'flame present' signal to the main computer. Because the system believes a fire is still burning when it shouldn't be, it shuts down completely as a safety precaution.