Medium Warning
94 on Viessmann Vitodens 222-W

Your boiler has lost communication with the temperature sensor in your hot water tank because of an electrical fault, meaning it cannot accurately monitor your solar heated water.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Technical description

Control mode - Solar: Cylinder temperature sensor shorted out

What causes this fault?

This fault occurs when the electrical circuit for the solar hot water sensor is completed prematurely, usually due to moisture ingress or damaged insulation. The most common reason is that the sensor probe has failed internally or the wires connecting it to the boiler have become pinched or corroded, preventing the system from reading the water temperature.

This fault is more common during the summer months when solar thermal systems are under peak thermal load and high temperatures can accelerate the degradation of aging sensor cables.

Engineer required

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

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