Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Remove brown and yellow wires from CH sensor
Remove brown and yellow wires from CH sensor
Measurement:
Measure resistance between the terminals on the sensor.
The resistances measured will depend upon the boiler temperature, the table shows some typical measurements.
The working range is between 1.5-25kOhms.
The resistances measured will depend upon the boiler temperature, the table shows some typical measurements.
The working range is between 1.5-25kOhms.
| Temperature °C | Resistance in kOhms |
| 15-20 | 15.0-9.0 |
| 20-50 | 9.0-3.0 |
| 50-60 | 3.0-2.0 |
| 60-85 | 2.0-1.5 |
Isolate as per TOPs P4
and refit as necessary