Your boiler's internal computer brain cannot find its identity chip, which prevents it from operating safely.

Code plug not detected: Code plug version, condition and fitting. If OK replace control board.

What causes this fault?

This fault occurs when the boiler's main control board loses communication with a small, specialized chip called a coding plug that contains the unit's unique settings. The most common reason is that the plug has vibrated loose or become faulty, but it can also happen if moisture or a power surge has damaged the circuitry on the main control board.