Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
Selector Switch to Hot Water and Heating
Remove diverter valve motor
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Is the diverter valve motor spindle in the DHW position?
i.e. fully retracted