BoilerFaultCodes 4 (Flashing Light) Low
Boiler Fault Code 4 (Flashing Light)
Also written as 4FLASHINGLIGHT — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 4 (Flashing Light) appears across 1 boiler brand and 9 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is currently in standby mode and is working exactly as it should while waiting for a signal from your thermostat to provide heating. (As reported on Ferroli Tempra 12 18)
Pick your boiler brand for the 4 (Flashing Light) fix
Source
Information for the 4 (Flashing Light) fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026