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
Disconnect plug marked M11

Measurement:

Test 1:
With CH temperature selector set to maximum, measure the resistance across the red wire (connection D), and the black wire (connection F).
Resistance measured should be approximately 10 kOhms.
Turn CH temperature selector to minimum.
Resistance should reduce to less than 100 Ohms.
Test 2:
With CH temperature selector set at minimum, measure the resistance across the white wire (connection E), and the black wire (connection F).
Resistance measured should be approximately 10 kOhms.
Turn CH temperature selector to maximum.
Resistance should reduce to less than 100 Ohms.