Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Ensure appliance is cool
Set flow rate to approx. 3 litres a minute
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the pump run?
Do not take noise or vibration as a sign of satisfactory pump operation.
Note:
If the vent plug is removed to ascertain if the pump is running take precautions to ensure any water discharged is safely contained.