Set Appliance State:

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

Observation:

Visually inspect the diverter valve spindle - it should be free from any sign of leaks.
Press in the central pin (a tool may be required as it may require quite firm pressure).
The central pin should move in approximately 10mm.
Remove the pressure and the central pin should spring back out approximately 10mm to its original position.
Is the diverter valve body satisfactory?