Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect plug from DHW sensor (purple and grey 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.
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