Boiler Fault Code 91:2

Also written as 912 — same fault.

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

Fault code 91:2 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 experiencing a communication issue with the accessory that controls different temperature zones in your home, often caused by a temporary wiring hitch or a sensor problem. (As reported on Viessmann Vitodens 200)