High Lockout
FC on Viessmann Vitodens 050-W

Your boiler has shut down because it cannot correctly control the flow of gas needed to stay alight.

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

Burner in fault position. Modulation coil faulty. Check the gas train.

What causes this fault?

This fault occurs when the boiler's control system loses the ability to precisely adjust the amount of gas entering the burner. The most common cause is a failure in the electrical coil that moves the internal gas valve, meaning the boiler can no longer maintain a safe and steady flame to heat your home.

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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