Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove leads to return thermistor
If required attach temperature clamp to the return pipe
to determine temperature range
If required attach temperature clamp to the return pipe
to determine temperature range
Measurement:
Measure for resistance across the exposed pins of the return thermistor.
The resistance depends on temperature and should
conform to the table below:
The resistance depends on temperature and should
conform to the table below:
| Flow Temperature °C | Resistance in kOhms |
| 10 - 20 | 19.0 - 12.0 |
| 20 - 30 | 12.0 - 8.0 |
| 30 - 40 | 8.0 - 5.0 |
| 40 - 50 | 5.0- 3.8 |
| 50 - 60 | 3.8 - 2.5 |
| 60 - 70 | 2.5 - 1.7 |
| 70 - 80 | 1.7 - 1.3 |
Isolate as per TOPs P4
and refit as necessary