F.0 High

Vaillant F.0 Fault Code

Also written as F0 — same fault.

The Vaillant F.0 fault code means: your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit due to a sensor or wiring connection fault.. It appears on 23 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: Flow–NTC open circuit. NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics

What causes the Vaillant F.0 fault?

This fault occurs when the boiler's control system loses the signal from the sensor that monitors the temperature of the water flowing out to your radiators. The most common reason is that the sensor itself has failed internally or the electrical wiring connecting it to the main control board has become loose or damaged. Without this vital temperature data, the boiler shuts down as a safety precaution to prevent overheating.

Typical repair cost £100-£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.0 fault code

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

Source

Vaillant F.0 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