How much does it cost to fix Vaillant error code F.01 / F.1?

Typical repair cost for the Vaillant F.01 / F.1 fault is £95-180 including labour.

F.01 / F.1 High

Vaillant F.01 / F.1 Fault Code

Q: What does the Vaillant F.01 / F.1 fault code mean?

Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water returning to the unit.

Also written as F01F1 — same fault.

The Vaillant F.01 / F.1 fault code means: your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water returning to the unit.. It appears on 4 Vaillant models in our database.

Technical description: Return temperature sensor interruption

What causes the Vaillant F.01 / F.1 fault?

This fault occurs when the boiler's main control board loses the electrical signal from the sensor that monitors the temperature of the water returning from your radiators. The most common reason is a physical failure of the sensor itself, but it can also be caused by loose or damaged internal wiring that prevents the signal from reaching the computer.

Typical repair cost £95-180 (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.01 / F.1 fault code

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

Source

Vaillant F.01 / F.1 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 27 April 2026