High Lockout
E129 on Potterton Promax HE

Your boiler has failed to keep its flame lit while trying to automatically adjust its settings for efficient burning.

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

Loss of flame during calibration

What causes this fault?

This fault occurs when the boiler's internal computer tries to adjust the gas and air mixture to ensure it is burning fuel as efficiently as possible, but the flame goes out during the process. The most common reason is that the sensor responsible for 'seeing' the flame is dirty or worn out, or the gas valve isn't providing a steady enough flow for the boiler to complete its self-check. Because the boiler cannot guarantee a safe and efficient burn, it shuts down for safety.

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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