81 High

Boiler Fault Code 81

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code 81 appears across 5 boiler brands and 17 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that a critical safety sensor responsible for monitoring exhaust gases has become disconnected, so it has safely shut itself down to prevent operation until the issue is fixed. (As reported on Atag Premier)

Pick your boiler brand for the 81 fix

Atag 81 6 models Ideal 81 6 models Keston 81 2 models Navien 81 1 model Unical 81 2 models

Source

Information for the 81 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 7 July 2026