Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

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 top of the actuator i.e. farthest left as look at the head when in situ.