F.13 Low

Viessmann F.13 Fault Code

Also written as F13 — same fault.

The Viessmann F.13 fault code means: your boiler has lost its connection to the sensor that measures the temperature outside, meaning it may not know how hard it needs to work to heat your home.. It appears on 4 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: Lead break, outside temperature sensor
Typical repair cost £90-180 (including labour)

DIY fix possible

Check the outside sensor for any obvious signs of physical damage or loose casingInspect the visible cable running from the sensor for any breaks or animal damageTry resetting the boiler to see if the fault clears (it may be a temporary software glitch)

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Viessmann models that show the F.13 fault code

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

Source

Viessmann F.13 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