Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the two spade connectors from the return thermistor
Measurement:
Measure the resistance between the two terminals on the return sensor.
Resistances vary with temperature and should conform approximately to the table below:
Resistances vary with temperature and should conform approximately to the table below:
| Temperature °C | Resistance in ohms | 0-10 | 28.8k - 19.0k |
| 10-20 | 19.0k - 12.0k |
| 20-30 | 12.0k - 8.0k |
| 30-40 | 8.0k - 5.0k |
| 40-50 | 5.0k - 3.5k |
| 50-60 | 3.5k - 2.5k |
| 60-70 | 2.5k - 1.7k |
| 70-80 | 1.7k - 1.2k |
| 80-90 | 1.2k - 860 |
| 90-100 | 860 - 700 |
Isolate as per TOPs P4
and refit as necessary