Your boiler is struggling because a small internal identification chip that tells the system how to operate correctly has come loose or is not being recognised.

Coding plug not detected.

What causes this fault?

This fault occurs when the boiler's main control board loses communication with a small memory chip called a code plug, which contains the boiler's essential operating software. The most common reason is a loose connection between the two components, though it can also be caused by a complete electronic failure of the chip or the circuit board itself.