Set Appliance State:

Mains Power Off
Ensure DHW mode is turned on in User Control
Run hot water tap at flow rate of 3 l/min
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 confirm operation take care to ensure any water discharged is safely contained.