Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove eight way connector from PCB
Measurement:
Measure the resistance across the purple wires.
Resistance should be approx as per table:
Resistance should be approx as per table:
| Boiler | Resistance |
| 9 HE or HE 30 | 117 Ohms | 12 HE or HE 40 | 40 Ohms | 15 HE or HE 50 | 35 Ohms | 18 HE or HE 60 | 35 Ohms |
Isolate as per TOPs P4
and refit as necessary