Boiler Fault Code 73:1 to 73:6

Also written as 731TO736 — same fault.

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

Fault code 73:1 to 73:6 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 the hot water cylinder's circulation pump is running on a preset timed cycle to prevent legionella or keep the water warm, rather than responding to a specific heating demand. (As reported on Viessmann Vitodens 200)