High Lockout
F.26 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler has detected an electrical issue with the gas valve, meaning it cannot safely control the fuel needed to create a flame.

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

Error with gas valve – possible no function

What causes this fault?

This fault occurs when the boiler's main computer loses electrical communication with the gas valve, which acts as the 'tap' for the fuel. The most common reason is an internal electrical failure within the valve's motor or a loose connection in the wiring that prevents the valve from opening or closing as instructed.

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 →F.62View →

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