Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Selector switch to DHW position
CH temperature selector to minimum
DHW Preheat selector to OFF position
Remove diverter valve head and place in a safe location
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Observe the diverter valve head spindle.
With selector switch in DHW position spindle should be retracted.
Move selector switch to CH position.
Spindle should now extend.