Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove connector plug from DHW temperature sensor (green leads)

Measurement:

Measure resistance across the exposed terminals of the sensor.
The resistance depends on temperature and should conform to the table below:
Temperature °CResistance in kOhms
20 - 306.1 - 3.8
30 - 404.0 - 2.5
40 - 502.7 - 1.6
50 - 601.8 - 1.0
60 - 701.3 - 0.7
70 - 800.9 - 0.5