F.64 High

Vaillant F.64 Fault Code

Also written as F64 — same fault.

The Vaillant F.64 fault code means: your boiler has detected an electrical fault within its internal sensors or control board, which has caused the system to shut down for safety.. It appears on 46 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: Electronics/sensor fault: Short-circuit in flow or return sensor or electronics defective

What causes the Vaillant F.64 fault?

This fault occurs when the boiler's internal computer receives conflicting or impossible signals from its temperature sensors. It is usually caused by a short circuit in the wiring or a total failure of the NTC sensors that measure water temperature, but it can also indicate that the main control board is no longer processing data correctly. To prevent overheating, the boiler immediately shuts down until the faulty electrical component is replaced.

Typical repair cost £120-£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.64 fault code

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

Source

Vaillant F.64 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