High Lockout
30 on Viessmann Vitodens 333

Your boiler has stopped working because its internal temperature sensor has developed an electrical fault and can no longer safely monitor the heat level.

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 blocked - Boiler temperature sensor shorted out

What causes this fault?

This fault occurs when the electrical connection inside the boiler's main temperature sensor fails, causing it to send an incorrect signal to the control board. The most common reason is internal wear or a moisture leak that has damaged the sensor's wiring, making it impossible for the system to safely monitor the water temperature.

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

38View →F2View →F3View →

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