Boiler Fault Code 79:1

Also written as 791 — same fault.

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

Fault code 79:1 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's electronic brains are experiencing a communication conflict or an internal memory error, which may cause the system to stop working correctly. (As reported on Viessmann Vitodens 300-W)