Set Appliance State:

Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Boiler mains switch ON
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 blue and black leads at the diverter valve connector X6a at the PCB.