Set Appliance State:

Gas Off
Gas On; Pilot On
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Link pins 1 and 2 of five pole connector on mounting frame
Selector switch ON
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Does the fan continue to run at high speed and commence the ignition sequence, or does it return to slow fan ?
Note:
This test bypasses all external controls