Set Appliance State:

Mains Power Off
Gas Off
Set Multimeter to AC Voltage Set meter to measure AC Volts
Turn Hot Water Tap On
Selector Switch in HOT WATER position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Depress the Gas Control Knob. Allow the Boiler to execute its purge delay period and measure the voltage across PCB connector D connections 55 (Blue wire) and connection 56 (Brown wire).
Note. Gas Control Knob has to be fully depressed while measurement is being taken.