F.670 Low

Viessmann F.670 Fault Code

Also written as F670 — same fault.

The Viessmann F.670 fault code means: your boiler is struggling to communicate with the sensor that tracks heat from your solar panels, meaning it cannot use stored solar energy to help heat your home.. It appears on 2 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: No solar central heating backup. Lead break, buffer temperature sensor TS3.
Typical repair cost £120-200 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Viessmann models that show the F.670 fault code

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

Source

Viessmann F.670 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 7 July 2026