Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
If not already done, reconnect LV2 connector to the PCB
Disconnect inline connector between PCB and DHW flow sensor and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the display now operate?
(A fault code may be displayed)