Set Appliance State:

Mains Power Off
CH Demand
CH Thermostat up to MAX on Boiler
On/Off switch ON
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Does the fan run?
Note:
If power has been turned off to the appliance then approximately 10 seconds will elapse before fan will start.