Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Boiler mains switch ON
CH demand
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the ignition sequence to commence and burner to ignite.
Measure the voltage across the red and grey leads at the diverter valve connector at the upper centre of the PCB.