Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect connector from X22 on the PCB
Measurement:
Measure resistance across the two blue leads at connector.
The resistance will vary according the boiler temperature but should conform approximately to the table below:
The resistance will vary according the boiler temperature but should conform approximately to the table below:
| Temperature °C | Resistance in kOhms |
| 20 | 22 |
| 30 | 9.4 |
| 40 | 7 |
| 50 | 7.3 |
| 60 | 4.7 |
| 70 | 3.8 |
| 80 | 2.8 |
Isolate as per TOPs P4
and refit as necessary