Boiler Fault Code 81:2

Also written as 812 — same fault.

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

Fault code 81:2 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 having trouble communicating with its external radio clock module, meaning it may not know the correct time or date for your heating schedule. (As reported on Viessmann Vitodens 200)