BoilerFaultCodes 221 / E9 High
Boiler Fault Code 221 / E9
Also written as 221E9 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 221 / E9 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 detected that a safety device is not plugged in correctly, causing it to shut down to prevent unsafe operation. (As reported on Worcester Bosch Greenstar CDi Compact)
Pick your boiler brand for the 221 / E9 fix
Source
Information for the 221 / E9 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