BoilerFaultCodes 811 Medium
Boiler Fault Code 811
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 811 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has failed to reach the high temperature required to kill potential bacteria in your hot water supply, so it is alerting you that the water may not be safe for certain uses. (As reported on Worcester Bosch Greenstar 4000)
Pick your boiler brand for the 811 fix
Source
Information for the 811 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 27 April 2026