Boiler Fault Code 2921 -

Also written as 2921 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 2921 - appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has been left in a professional testing mode, meaning it is currently running at a fixed output rather than responding to your heating controls. (As reported on Worcester Bosch Greenstar 2000)