Your boiler's internal computer memory chip is loose or missing, meaning it cannot identify which model it is supposed to be.

Code plug not detected.

What causes this fault?

This fault occurs when the small memory chip, known as a code plug, becomes loose or fails to communicate with the boiler's main control board. Without this chip, the boiler essentially forgets its own identity and safety settings, leading to an immediate shutdown for security reasons. The most common cause is either physical vibration loosening the connector or an electrical failure within the chip itself.