Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Selector Switch to Hot Water and Heating
Remove the blue and red wires from the selector switch
Attach crocodile clips to the exposed terminals
Remove the blue and red wires from the selector switch
Attach crocodile clips to the exposed terminals
Measurement:
Test 1:
Measure the resistance between the 2 exposed terminals.
Expect approximately 1MOhm or greater.
Test 2:
Turn the selector switch to the reset position while observing the multimeter.
Continuity / zero resistance should be measured between the 2 terminals when the switch is in the reset position.
Are the resistances as expected?
Measure the resistance between the 2 exposed terminals.
Expect approximately 1MOhm or greater.
Test 2:
Turn the selector switch to the reset position while observing the multimeter.
Continuity / zero resistance should be measured between the 2 terminals when the switch is in the reset position.
Are the resistances as expected?
Isolate as per TOPs P4
and refit as necessary