Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Isolate cold feed to boiler
Ensure No demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the display still show the DHW symbol after self-check & purge cycle has completed?
Cancel the purge cycle if required as per previous test.