High Lockout
59 on Viessmann Vitodens 333

Your boiler is unable to heat your hot water because a sensor that monitors the temperature of the water cylinder has stopped communicating with the system.

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/outlet sensor lead break

What causes this fault?

This fault occurs when the boiler loses its connection to the sensor responsible for monitoring the hot water storage temperature. The most common reason is a physical failure of the internal sensor probe or damage to the wiring harness, causing an electrical 'break' that prevents the control board from receiving data.

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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