Set Appliance State:
Mains Power Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect plug from CH sensor (yellow leads)
Measurement:
Measure resistance across the exposed terminals of the sensor.
The resistance measured will depend on the boiler temperature.
The hotter the boiler, the lower the resistance.
Refit leads after test.
The resistance measured will depend on the boiler temperature.
The hotter the boiler, the lower the resistance.
| Temp °C | Resistance in kOhms | 20 - 30 | 8 to 16 |
| 30 - 40 | 6 to 10 |
| 40 - 50 | 3.9 to 8 |
| 50 - 60 | 2.5 to 5.5 |
| 60 - 70 | 1.5 to 3.0 |
Isolate as per TOPs P4
and refit as necessary