Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to DC Volts Set meter to measure DC Volts
Gain access to PCB (use Insulation Mat as required)
Remove fan connector from fan assembly and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage between the brown wire
on X8 to a suitable earth point.
Voltage should be approximately 28V DC.