Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Set temperature selector to MAX
Release the front fascia by gently prising up the retaining latches at the top of the fascia

Measurement:

Test 1.
Measure resistance between the back of the potentiometer and the L/H connection on the back of the switch.
Expected resistance zero Ohms.
Test 2.
Repeat test between the back of the potentiometer and the R/H connection on the back of the switch.
Expected resistance approximately 230 Ohms.