Set Appliance State:

Mains Power Off
DHW Demand
Gas On
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 pump satisfactory.
Note:
If the vent plug is removed to ascertain if the pump is running take precautions to ensure the water discharged is safely contained.