Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect plug connector (marked ST16) from PCB

Measurement:

Check resistance across connections 5 & 6 (orange wires).
Note:
Care should be taken that probe tips do not touch each other when taking measurement as a false reading will be given. Also ensure that other end of leads are connected to the overheat thermostat.