Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove control box cover if necessary
Remove the 20 way connector (ST9) from the right hand side of the PCB
If available use the Worcester test PCB to assist resistance test

Measurement:

Measure the resistance across the two red wires terminals
5 and 6 counting left to right on the 20 way connector.
Note:
Colours may vary from those shown but terminal positions
will remain the same.