Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove connector from the return thermistor
If required attach temperature clamp to the return pipe
to determine temperature range
If required attach temperature clamp to the return pipe
to determine temperature range
Measurement:
Measure for resistance across the exposed pins of the return thermistor.
Isolate as per TOPs P4
and refit as necessary