73:1 to 73:6 Low

Viessmann 73:1 to 73:6 Fault Code

Also written as 731TO736 — same fault.

The Viessmann 73:1 to 73:6 fault code means: 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.. It appears on 5 Viessmann models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: During the time program 1x/h ON for 5 minutes up to 6x/h ON for 5 minutes

What causes the Viessmann 73:1 to 73:6 fault?

This is not a mechanical failure but rather a status notification triggered by the boiler's internal anti-legionella or comfort settings. It occurs when the control system activates the domestic hot water circulation pump for short, periodic bursts to keep water moving through the pipes. This ensures hot water is instantly available at the taps and prevents water from stagnating in the cylinder.

Typical repair cost £0-80 (including labour)

DIY fix possible

This is often a status notification rather than a breakdown.Check your hot water time program settings on the control panel.Ensure your legionella protection or DHW circulation pump settings match your daily needs.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

Viessmann models that show the 73:1 to 73:6 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann 73:1 to 73:6 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

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