Set Appliance State:
Set Multimeter to DC Volts 
CH Demand
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
With the fan running measure the voltage between the yellow wire at CON11 on the PCB to a suitable earth point.
Voltage should be approximately 28V DC.
Voltage should be approximately 28V DC.
Isolate as per TOPs P4
and refit as necessary