Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove both wires from the frost thermostat
Measurement:
Measure the resistance between the terminals of the frost thermostat.
Is the resistance measured open circuit or continuity/zero resistance?
Note:
Image shows the frost thermostat removed for clarity but the test is carried out with it attached to the return pipe.
Is the resistance measured open circuit or continuity/zero resistance?
Note:
Image shows the frost thermostat removed for clarity but the test is carried out with it attached to the return pipe.
Isolate as per TOPs P4
and refit as necessary