Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove yellow wires from DHW 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