Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the 5 pin connector from the PCB
Isolate the incoming DHW
(it is advisable not to use the appliance isolation valve as these are prone to leaking when turned)
Isolate the incoming DHW
(it is advisable not to use the appliance isolation valve as these are prone to leaking when turned)
Measurement:
Measure the resistance between the 2 left hand grey wires.
Expect open circuit / O.L.
Is the resistance measured as expected?
Expect open circuit / O.L.
Is the resistance measured as expected?
Isolate as per TOPs P4
and refit as necessary