Boiler Fault Code 81:1

Also written as 811 — same fault.

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

Fault code 81:1 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 notifying you that it has automatically switched between heating and hot water mode based on the outside temperature. (As reported on Viessmann Vitodens 300-W)