Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Remove electrical connector from fan assembly, leave in a safe location
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance if required (press reset button for 2 seconds and release).
Measure for DC volts across pin 17 (purple lead) on connector X20 and
a suitable earth connection.
Expected voltage approximately 22.0 Vdc.
Note.
Ensure a good connection is made or misdiagnosis may occur.