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.

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.