Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Mains Isolator Switch (ON/OFF Switch) in ON position
Selector Switch in DHW Summer position
Hot Water Temperature Control set to Maximum
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Is the pump running?
Note:
Do not take noise or vibration as an indication of the pump running.