BoilerFaultCodes 809 High
Boiler Fault Code 809
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 809 appears across 2 boiler brands 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 lost the ability to accurately measure the temperature of the water inside its internal store, which prevents it from heating your water correctly. (As reported on Worcester Bosch Greenstar Heatslave II)
Pick your boiler brand for the 809 fix
Source
Information for the 809 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