F.37 High

Vaillant F.37 Fault Code

Also written as F37 — same fault.

The Vaillant F.37 fault code means: your boiler has stopped working because the fan that clears exhaust gases is not spinning at the correct speed or the sensor that monitors it has failed.. It appears on 9 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: (837/637 only) | The rotary speed of the fan is too high or too low | Air pressure switch defect; fan defect; electronics defect

What causes the Vaillant F.37 fault?

This fault occurs when the boiler's safety system detects that the fan is not moving at the correct speed to safely clear exhaust gases from the flue. The most common reasons are a mechanical failure within the fan motor or a fault with the sensor that monitors air pressure, preventing the boiler from firing for safety reasons.

This fault can be more frequent in winter, as high winds can sometimes create back-pressure in the flue that interferes with the fan's operation or the air pressure switch.

Typical repair cost £180-£450 (including labour)

Engineer required

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

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Vaillant models that show the F.37 fault code

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

Source

Vaillant F.37 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026