Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove diverter valve stepper motor & place in a safe position where it can be observed
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to ignite and run on CH operation.
Confirm that the stepper motor spindle has moved to its CH position?
Note.
CH position will be when the stepper motor spindle has moved
to its retracted position.