Your boiler has detected a flame when there shouldn't be one, or the sensor incorrectly thinks a fire is lit, causing it to shut down for safety.

Extraneous flame

What causes this fault?

This fault occurs when the boiler's control system detects a flame signal at a time when the gas should be turned off. This is often caused by a faulty sensor sending a false signal, a gas valve that is leaking slightly, or a glitch in the main circuit board that misinterprets electrical background noise as a fire.