High Lockout
S.1 on Vaillant ecoTEC 65kW

Your boiler is trying to start up but the internal fan is not spinning properly, preventing the heating from firing up.

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

Fan start-up error

What causes this fault?

This fault occurs when the boiler's control system sends a signal to the fan to begin spinning, but it fails to reach the required speed to safely start the ignition process. The most common reasons are a build-up of debris or moisture inside the fan casing, or a communication failure between the main control board and the fan motor.

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

S.2View →S.3View →

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