Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the two leads (blue) from the return sensor
Measurement:
Measure the resistance between the sensor terminals, also measure the approximate temperature at the sensor location.
The resistance will vary according the boiler temperature but should conform to the table below at the appropriate temperature to ensure it is within range and in calibration
The resistance will vary according the boiler temperature but should conform to the table below at the appropriate temperature to ensure it is within range and in calibration
| Temperature °C | Resistance in kOhms | 20 | 10 |
| 30 | 6.6 |
| 40 | 5.8 |
| 50 | 3.1 |
| 60 | 2 |
| 70 | 1.5 |
| 80 | 1.1 |
Isolate as per TOPs P4
and refit as necessary