Set Appliance State:

Ensure NO demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Test 1:
Are any symbols shown on the display?
(if not, press the power button once briefly)
Test 2:
Reset the appliance.
(press and hold the power button for 4 seconds then release)
As the appliance turns on or resets multiple symbols in the display will be shown briefly before the appliance commences its self-check.
Does the display illuminate and multiple symbols display briefly?