F.012 High

Vaillant F.012 Fault Code

Also written as F012 — same fault.

The Vaillant F.012 fault code means: your boiler is having trouble reading the temperature of your hot water, which means it has stopped providing hot water to your taps to prevent the system from overheating.. It appears on 3 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: Fault in the electrical connection for the domestic hot water connection temperature sensor. Domestic hot water temperature sensor defective.
Typical repair cost £120-200 (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.012 fault code

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

Source

Vaillant F.012 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