Set Appliance State:

Mains Power Off
Gas On; Pilot On
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
On/Off Switch ON
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across pins 4 and a suitable neutral to the pump on the PCB
Expect 240Vac approximately.