Your boiler is failing to switch between providing hot water and heating, meaning your central heating may not turn on even when the system is calling for it.

Diverter valve does not operate (CH test) / 230V at pin 3 of terminal X7 (Brown wire)

What causes this fault?

This fault occurs when the boiler's internal mechanism for switching between heating and hot water becomes stuck or fails to respond to electrical signals. The most common reason is that the motor responsible for moving the valve has burnt out, or the valve itself has become jammed with debris from the heating system's water.