High Lockout
63:0 on Viessmann Vitodens 333-F

Your boiler is failing to communicate properly with the equipment used to heat your hot water tank, meaning you may lose hot water.

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

Without auxiliary function for DHW loading

What causes this fault?

This fault occurs when the boiler's main control board loses its electronic connection with the components responsible for heating your hot water cylinder. The most common reason is a breakdown in the communication module or a faulty sensor that prevents the boiler from knowing the water temperature in the tank. Without this data link, the boiler stops heating the cylinder as a safety precaution.

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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