High Lockout
59 on Viessmann Vitodens 100-W / 200-W

Your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit, usually due to a fault in a sensor or its wiring.

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

No DHW heating: Cylinder temperature sensor 2 lead break

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor that monitors the heat of the water leaving the unit. It is usually caused by a physical break in the internal wiring or the sensor itself failing due to wear and tear. Because the boiler cannot safely confirm the water temperature, it shuts down to prevent the system from overheating.

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

51View →58View →A9View →

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