Set Appliance State:

Mains Power Off
Gas On; Pilot On
Selector Switch OFF
Gas Control Knob in Main Burner position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan to run high speed then reduce to slow speed.
(This should take approximately 30 seconds)
Selector Switch ON.
Create CH Demand.
Does the Fan speed increase?