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
Hinge down the PCB housing
Reconnect fan connector at the fan if you have not already done so
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow fan to start to run.
Measure for DC volts across the green wire of
illustrated connector to a suitable neutral.
Expected voltage approx. 8V DC.