Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove connector J6 from main PCB
Measurement:
Measure the resistance across the red wire (Note: use the red wire on the far left) and the black wire at the disconnected connector J6 (black connector).
The resistance will depend upon the temperature of the boiler the hotter the boiler the lower the resistance. The resistance should conform to the table below.
Temperature°C | Resistance kOhms |
| 20-25 | 11.4-12.5 |
| 25-30 | 9.7-11.4 |
| 30-35 | 7.5-9.7 |
| 35-40 | 6.5-7.5 |
| 40-50 | 5.0-7.2 |
| 50-60 | 3.0-5.0 |
| 60-70 | 2.5-3.0 |
| 70-80 | 1.8-2.5 |
| 80-90 | 1.3-1.8 |
Isolate as per TOPs P4
and refit as necessary