High Lockout
B1 on Worcester Bosch CDi Classic

Your boiler's computer memory chip is loose or missing, meaning the system doesn't know which model it is and has stopped working for safety.

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

Code plug not detected .

What causes this fault?

This fault occurs when the boiler's control board loses communication with a small, removable chip called the code plug. It is usually caused by the plug vibrating loose over time or failing due to a hardware fault on the main circuit board. Without this chip, the boiler cannot verify which model it is or what safety settings to use, so it shuts down immediately.

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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