Boiler Fault Code 1 flash green

Also written as 1FLASHGREEN — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code 1 flash green appears across 3 boiler brands and 6 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 it is heating up too quickly or getting too hot, usually because the water isn't moving through the system properly. (As reported on Baxi 800 Heat (range))