Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Turn Hot Water Tap On

Measurement:

Disconnect the two wires from the water section rear microswitch.
Measure the resistance across the microswitch terminals.
Repeat the test with the water section front microswitch.
Reconnect wires after test.