How much does it cost to fix Vaillant error code F.64?

Typical repair cost for the Vaillant F.64 fault is £120-£450 including labour.

F.64 High

Vaillant F.64 Fault Code

Q: What does the Vaillant F.64 fault code mean?

Your boiler has detected an electrical fault within its internal sensors or control board, which has caused the system to shut down for safety.

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 53 Vaillant models in our database.

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.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →

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 27 April 2026