High Lockout
F.26 on Vaillant ecoTEC Pro 28

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.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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 this 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.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.27View →F.28View →F.29View →

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