Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect fan connector plug from the PCB
Measurement:
Test 1:
Measure resistance across the two violet leads of the disconnected plug.
Expected resistance approximately 35 Ohms.
Test 2:
Measure resistance from either of the violet leads on the disconnected plug to a suitable earth point.
Expected resistance open circuit.
Note:
Values above for normal fan - If boiler is pre serial number AHHU8330001 and has a Sifan fan fitted with additional connections for a capacitor CLICK HERE.
Measure resistance across the two violet leads of the disconnected plug.
Expected resistance approximately 35 Ohms.
Test 2:
Measure resistance from either of the violet leads on the disconnected plug to a suitable earth point.
Expected resistance open circuit.
Note:
Values above for normal fan - If boiler is pre serial number AHHU8330001 and has a Sifan fan fitted with additional connections for a capacitor CLICK HERE.
Isolate as per TOPs P4
and refit as necessary