Your boiler has detected a problem with how it tracks its own flame, causing it to shut down for safety purposes.

Fault in flame monitoring

What causes this fault?

This fault occurs when the boiler's internal computer is unable to verify that a flame is present, even if the burner has ignited correctly. It is usually caused by a dirty or corroded sensor that can no longer send a clear signal back to the control board, or a fault within the wiring and electronics that manage safety checks. Consequently, the boiler shuts down because it cannot confirm it is operating safely.