Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Turn Hot Water Tap On
Remove the plastic cover from the hot water
microswitch and disconnect the wires connected to it
Set flow rate to 2.8 litres a minute

Measurement:

Measure the resistance across the hot water microswitch terminals.
Resistance should be short circuit.