BoilerFaultCodes 81:3 Low
Boiler Fault Code 81:3
Also written as 813 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 81:3 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 having trouble synchronizing its internal clock with an external control system, which might affect your heating schedules. (As reported on Viessmann Vitodens 300-W)
Pick your boiler brand for the 81:3 fix
Source
Information for the 81:3 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