Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
Rotary Switch in OFF position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across the mains live (Brown wire) connection marked L and the mains neutral (Blue wire) connection 2 marked N on the main terminal block.