F.46 Medium

Vaillant F.46 Fault Code

Also written as F46 — same fault.

The Vaillant F.46 fault code means: your boiler has detected an electrical fault with the sensor that monitors the temperature of the incoming cold water, preventing it from calculating how much heat is needed.. It appears on 1 Vaillant model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Short circuit: Additional temperature sensor at the water inlet
Typical repair cost £120-220 (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.46 fault code

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

Source

Vaillant F.46 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