Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
CH Demand
Mains Reset Switch OFF
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Mains reset switch ON.
Measure voltage across pin 4 of fan connector and a suitable earth point.
After approximately 5 - 10 seconds fan control voltage should increase from approximately 1.0Vdc to 5.0Vdc or greater.