High Lockout
S.16 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler's fan is still spinning after the hot water has been turned off, preventing the system from restarting safely.

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

DHW mode – fan overrun error

What causes this fault?

This fault occurs when the boiler’s software detects that the fan is still spinning at high speed after the demand for hot water has ended. The most common reason is a communication error between the fan and the control board, where the fan fails to slow down to a safe standby speed. It can also be caused by a sticking signal wire or a fault within the fan’s internal electronic 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

F.32View →S.31View →

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