Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove Pump Screw
Selector Switch in DHW Summer position
Hot Water Thermostat set to Maximum
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

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