Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the diverter valve actuator from the diverter valve body

Observation:

Check for free movement of the diverter valve spindle.
It should be possible to depress the diverter valve spindle by finger pressure.
The CH position of the valve is when the spindle is pushed in.

Note:
For clarity the graphic shows the valve removed but it is possible to check the spindle with the valve in situ and the actuator removed.