High Lockout
b5 on Viessmann Vitodens 050-W

Your boiler has experienced an internal communication error or processor glitch that is preventing it from running properly.

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

Control mode: Internal fault

What causes this fault?

This fault occurs when the boiler's internal computer experiences a breakdown in communication with its own components or sensors. It is usually caused by a hardware failure within the main control board or a loose connection in the internal wiring, meaning the boiler can no longer verify it is safe to operate.

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

b1View →b7View →F4View →

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