Set Appliance State:

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

Measurement:

Depress the Gas Valve Control Knob.
Is there Mains Voltage across connector M4 connection 21 (Brown wire) and connection 20 (Blue wire) on the main PCB?