Boiler Fault Code 21:0

Also written as 210 — same fault.

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

Fault code 21:0 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 is simply notifying you that a routine service is due based on its operating hours. (As reported on Viessmann Vitodens 200)