High Lockout
9 (Flashing) on Potterton Envoy 30

Your boiler has shut itself down for safety because it failed to light or detected an internal problem.

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

Boiler at lock-out

What causes this fault?

This fault occurs when the boiler has tried to ignite several times but failed to establish a stable flame. The most common reason is a lack of fuel reaching the burner, often due to a faulty gas valve or worn-out ignition sparks that can no longer light the gas safely.

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.

Find a Gas Safe engineer
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