Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Expose PCB by removing plastic control box cover.
Remove connector B from PCB

Measurement:

Measure the resistance between connections B9 (Blue wire) and B8 (Black wire) at disconnected plug whilst turning the potentiometer throughout its entire range.
Resistance should vary approximately between 2.1 kohms and 2.3 kohms.
Note:
Test carried out at disconnected plug not PCB.