Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
DHW demand from programmer
DHW temperature selector to high setting
Ensure hot water storage vessel is calling for heat
Gain access to PCB (use Insulation Mat as required)
Remove electrical connector from diverter valve and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Boiler On/Off Switch On.
Allow fan to run and burner to ignite.
Measure the AC voltage between the two outer purple wires of the diverter valve connector, terminals 1 and 3.
Expect approximately 30 VAC.
Note: It can be difficult to test in the top of the connector, access to test can also be gained though the small holes on the underside of the connector as highlighted on the right.