Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove diverter valve head from the body
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to fire briefly in CH mode.
Isolate Mains Power to appliance as per TOPs P4

Press the diverter valve spindle with a screwdriver - it should push back to the fully retracted position.
Does the diverter valve spindle push in to the fully retracted position? (i.e. spindle fully retracted)
Note.
It may take approximately 40 seconds for the boiler to recognise a demand, this will depend upon the boiler status.
(Status code guidance CLICK HERE)