Set Appliance State:

Mains Power Off
Gas On; Pilot On
CH Demand
Selector Switch in CH & HW position.
CH Thermostat to Max.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Run the Central Heating for approximately two minutes and then remove the heating demand.
Does the Water Pump Overrun?
Note:
Do not take noise or vibration as indication of pump running.