F38 Low

Viessmann F38 Fault Code

The Viessmann F38 fault code means: your boiler has lost its connection to the sensor that measures the outdoor temperature, meaning it cannot automatically adjust its performance based on the weather.. 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: Lead break, outside temperature sensor (secondary check)
Typical repair cost £100-180 (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 F38 fault code

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

Source

Viessmann F38 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