High Lockout
A8 on Viessmann Vitodens 200-W

Your boiler's main internal computer has lost touch with the display panel, meaning the controls cannot talk to the heating unit.

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

Communication fault between PCB and programming unit (user interface)

What causes this fault?

This fault occurs when the data link between the boiler's main brain and the control screen is broken or interrupted. The most common reason is a loose internal connection or a failure of the delicate wiring that carries signals between the two components.

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

A9View →B0View →B7View →

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