Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove the lead from the return sensor
Remove the lead from the return sensor
Measurement:
Measure resistance across the exposed sensor terminals.
RETURN SENSOR RESISTANCE
Resistances vary with temperature and should conform approximately to the table below:
Note: Clicking on the resistance table will switch between table and graph view.
| Temperature Range (°C) | Resistance Range |
|---|---|
| 0°C to 10°C | 17.0kΩ - 10.2kΩ |
| 10°C to 20°C | 10.2kΩ - 6.3kΩ |
| 20°C to 30°C | 6.3kΩ - 4.0kΩ |
| 30°C to 40°C | 4.0kΩ - 2.6kΩ |
| 40°C to 50°C | 2.6kΩ - 1.7kΩ |
| 50°C to 60°C | 1.7kΩ - 1.2kΩ |
| 60°C to 70°C | 1.2kΩ - 860.0kΩ |
| 70°C to 80°C | 860.0kΩ - 620.0kΩ |
| 80°C to 90°C | 620.0kΩ - 450.0kΩ |
| 90°C to 100°C | 450.0kΩ - 340.0kΩ |
Isolate as per TOPs P4
and refit as necessary