Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector from primary sensor
Ensure primary heat exchanger is below 60° C
Carefully remove sensor.

Measurement:

Measure resistance across the exposed sensor terminals.
The resistance should conform to the table below:
Temperature °CResistance in kOhms
20-308.0-16.0
30-40 6.0-10.0
40-503.9-8.0
50-602.5-5.5
60-701.5-3.0

Refit sensor after test