F.26 High

Vaillant F.26 Fault Code

Also written as F26 — same fault.

The Vaillant F.26 fault code means: your boiler is unable to release gas into the burner because the internal electronic valve is not operating correctly, meaning it cannot ignite to provide heat or hot water.. It appears on 9 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: Fuel valve not working - Gas valve assembly stepper motor defective or not connected

What causes the Vaillant F.26 fault?

This fault occurs when the boiler's main control board tries to open the gas valve to start the heating process, but it receives no response from the valve's motor. The most common reason is that the internal electronic components of the gas valve have failed, or the wiring connecting it to the computer has become loose or damaged.

Typical repair cost £220-£380 (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.26 fault code

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

Source

Vaillant F.26 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