BoilerFaultCodes 91:3 Low
Boiler Fault Code 91:3
Also written as 913 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 91:3 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 receiving conflicting signals about how to heat your home because an external controller is trying to switch settings for several heating zones at once. (As reported on Viessmann Vitodens 300-W)
Pick your boiler brand for the 91:3 fix
Source
Information for the 91:3 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 27 April 2026