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
Mains Reset Switch OFF
Set temperature control to maximum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Mains reset switch ON.
Measure voltage across pin 1 of fan connector and a suitable earth point.
Expected voltage approximately 27 - 38 volts DC.
Note.
1. Ensure a good electrical connection is made at fan connector or misdiagnosis will occur.
2. Harness colours may change but test points will remain the same.