Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove ST9 connector from the PCB
If available use the Worcester test PCB to assist resistance test
If available use the Worcester test PCB to assist resistance test
Measurement:
Measure resistance across the right hand pair of orange wires terminals 19 & 20 counting left to right.
Isolate as per TOPs P4
and refit as necessary