Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Set Boiler Control Thermostat to MAX position
External controls calling for heat
Ensure boiler is cool
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Reset boiler as necessary.
Does the fan run with CH demand?