Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Set CH 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 CH switch.
Expected resistance approximately 5 - 200 ohms.
Test 2.
Repeat test between the back of the potentiometer and the R/H connection on the back of the CH switch.
Expected resistance approximately 200 - 500 Ohms.