Set Appliance State:

Mains Power Off
Gas On; Pilot On
CH Demand
Boiler On/Off Switch ON
CH Switch ON
DHW Switch in INSTANT position
Remove diverter valve microswitch cover
Ensure the diverter valve is in the water position (fully retracted) this can be achieved by running the hot water with the boiler switched off for a short period
CH Temperature Control in Maximum position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to operate with a CH demand for approximately 60 seconds. Does the diverter valve spindle extend fully towards the microswitches?