High
30 on Viessmann Vitodens 333-F

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.

What the manual says

Manufacturer manual

Burner blocked - Boiler temperature sensor shorted out

From this model's manual
Verified against the Viessmann Vitodens 333 F installation & service manual, page 92.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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