BoilerFaultCodes 21.0 Low
Boiler Fault Code 21.0
Also written as 210 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 21.0 appears across 2 boiler brands and 8 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning This code indicates that your boiler is currently running at its maximum factory-set heating capacity and is likely a status display rather than a mechanical failure. (As reported on Grant Vortex 15-20)
Pick your boiler brand for the 21.0 fix
Source
Information for the 21.0 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