Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect flow thermistor and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

As boiler will immediately enter fault code
it will try to run the fan.
Does the fan run?
Note:
Boiler may need resetting next time power is restored.