Set Appliance State:

Gas Off
Set Multimeter to AC Volts Set meter to measure AC Volts
Isolate Mains Power to appliance as per TOPs P4
Water heater switch set to constant
Set thermostat to MID position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across connection 4 (blue lead) and connection 8 (brown lead) on the control module.