Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Boiler ON/OFF switch OFF
CH thermostat to MAX position
Remove Pump Vent Screw as Necessary
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Boiler ON/OFF switch ON.
Does pump run?
Note:
Do not take sound or vibration as sign of pump running.
If pump vent plug is removed to observe pump shaft then care should be taken that water does not drip on to control box.