Boiler Fault Code Lights: On Flash Flash

Also written as LIGHTSONFLASHFLASH — same fault.

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

Fault code Lights: On Flash Flash appears across 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that there is not enough water circulating inside it, which triggers a safety shutdown to prevent the internal components from overheating. (As reported on Potterton Suprima HE)