Set Appliance State:

Set Multimeter to DC Volts Set meter to measure DC Volts
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the DC voltage between pin 4 on connector X20 and an earth (use the copper pipe to the gas valve as earth).
Expect approximately 22 Vdc.
Is the voltage as expected?