Set Appliance State:

Mains Power Off
On/Off Switch OFF
DHW temperature selector to maximum position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Appliance On/Off switch On.
Reset lockout as necessary.
Observe the diverter valve head actuator lever.
Is it in, or does it change to the DHW position?
Note:
DHW position is when the lever is nearest to the front of the appliance.