Boiler Fault Code Red lockout indicator bulb

Also written as REDLOCKOUTINDICATORBULB — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code Red lockout indicator bulb appears across 1 boiler brand and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has failed to light the flame after multiple attempts, so it has automatically shut off its gas supply as a safety precaution. (As reported on Chaffoteaux System 40 60)