High Lockout
b9 on Viessmann Vitodens

Your boiler has likely been left in a testing mode used during installation or there is a fault with the gas ignition valve.

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

Installation in unfinished state - Fault in burner / Ignition valve

What causes this fault?

This fault typically occurs because the boiler's software thinks the setup process hasn't been finished or it has detected a physical failure in the gas delivery system. The most common reasons are a malfunctioning gas valve that cannot control the flow of fuel correctly or an ignition electrode that is failing to spark properly. In some cases, it may simply be that an engineer forgot to deactivate a specific 'commissioning mode' after a repair or installation.

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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