Boiler Fault Code 21.0

Also written as 210 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026

Fault code 21.0 appears across 2 boiler brands 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 is displaying a status code indicating it has reached its maximum heat output setting, which is a normal operational setting rather than an active fault. (As reported on Grant Vortex Eco)