Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect CN200 from the ignition PCB

Measurement:

Check for continuity (zero resistance) of the brown / red and blue wires, in turn, running from the fan to pins 4 and 5 of connector CN200.
Check the connectors and harness are in good overall condition.
Note:
The wire running from pin 5 changes from brown to red where the harness passes through the combustion chamber harness connector.