Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove the white spaded wires (1) from the CH sensor
Remove the white spaded wires (1) from the CH sensor
Measurement:
Measure the resistance across the terminals on the sensor.
The resistance measured will depend on boiler temperature and should conform approximately to the table below:
The resistance measured will depend on boiler temperature and should conform approximately to the table below:
| Temperature °C | Resistance in kOhms |
| 10-20 | 19.0-13.0 |
| 30-40 | 8.0-5.0 |
| 50-60 | 3.5-2.5 |
| 70-80 | 1.7-1.2 |
Isolate as per TOPs P4
and refit as necessary