High Lockout
EF on Viessmann Vitodens

Your boiler is continuing to detect a flame even after it has been told to shut down, which is a safety precaution to prevent gas issues.

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

Flame after a delay

What causes this fault?

This fault occurs when the boiler's sensors detect heat or a flame signal even after the gas supply should have been cut off. The most common reason is a gas valve that is failing to close fully or a faulty electrode that is sending a false 'flame present' signal to the main control board.

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

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