High Lockout
FA on Viessmann Vitodens 333

Your boiler has stopped working because the internal fan is spinning too fast during the startup process, preventing the burner from igniting 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

Burner in fault state. Fan speed too high at burner start. Cause: Check the fan, check the fan cables, check the fan control. Press E.

What causes this fault?

This fault happens when the boiler’s computer detects that the fan is spinning much faster than it should be while trying to light the burner. This usually occurs because the control signals between the fan and the main circuit board are disrupted, or the fan's internal speed sensor has developed a mechanical failure. Without the fan spinning at the precisely correct speed, the boiler cannot safely mix gas and air, so it shuts down as a safety precaution.

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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