Set Appliance State:

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

Measurement:

Measure the voltage across connection 6 (Yellow wire) and connection 7 (White wire) on connector PL6 on the PCB.