BoilerFaultCodes 856 High
Boiler Fault Code 856
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 856 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 ignite multiple times and has locked itself down for safety to prevent a buildup of unburnt fuel. (As reported on Worcester Bosch Greenstar Heatslave II)
Pick your boiler brand for the 856 fix
Source
Information for the 856 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