Set Appliance State:

Mains Power Off
On/Off Switch ON (Switch flush with the fascia on the appliance)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the display operate? (illuminates & text / info on screen)
Note:
If a fault code is shown make a note of it at this point as the next test requires the boiler to be reset. Guidance on fault codes is given after the next test.