Medium
48 on Viessmann Vitodens 333-F

Your boiler has lost communication with the temperature sensor that controls your second heating circuit, causing that specific zone to stop heating correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Mixer closes - Heating circuit M2 flow temperature sensor lead break

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 boiler can no longer receive data from the sensor monitoring the temperature of your second heating zone, such as underfloor heating. The most common reasons are a loose connection in the internal wiring, a broken cable, or the sensor itself failing due to age.

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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