Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
CH Demand
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Locate connector X20 on the PCB, center of the right hand edge.
Check voltage to earth on pin 17 (Red) of X20.
This is the power supply to the fan, there should be around 22vDC here at all times.
Check voltage to earth on pin 17 (Red) of X20.
This is the power supply to the fan, there should be around 22vDC here at all times.
Isolate as per TOPs P4
and refit as necessary