BoilerFaultCodes 221 High
Boiler Fault Code 221
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 221 appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has detected a loose connection or a fault in the sensor that monitors internal safety temperatures, causing it to shut down to prevent overheating. (As reported on Worcester Bosch 24/28/35 CDi MkII)
Pick your boiler brand for the 221 fix
Source
Information for the 221 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