High Lockout
b4 on Viessmann Vitodens 222-W

Your boiler has encountered an internal electronic communication error that is preventing it from monitoring its own performance correctly.

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

Emissions test mode - Internal fault analog converter

What causes this fault?

This fault occurs when the boiler's internal computer is unable to process the data it receives from its electronic sensors. The most common reason is a component failure on the main circuit board, which prevents the system from accurately measuring how the boiler is burning gas.

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

b0View →b8View →

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