BoilerFaultCodes 309 Low
Boiler Fault Code 309
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 309 appears across 1 boiler brand and 4 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 performing a normal operational cycle by heating both your radiators and your hot water tank, so there is no fault with your system. (As reported on Worcester Bosch 24/28/35 CDi MkII)
Pick your boiler brand for the 309 fix
Source
Information for the 309 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