Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the M1 connector from the PCB.
DHW Taps OFF

Measurement:

Test 1:
Measure the resistance across connections 14 (Black) and 13 (Blue) of the microswitch.
Resistance should be open circuit.
Test 2:
Measure the resistance across connections 14 (Black) and 12 (Brown) of the microswitch.
Resistance should be short circuit (zero resistance).