Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Selector switch set to DHW
DHW temperature control set to MAX
Preheat switched OFF
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow appliance to complete its self-test and display to show 0
Does the symbol d appear in the display with a DHW demand?