Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect EBUS wiring connections and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the EBUS external controls disconnected does the boiler respond to a CH demand?
Note.
Ensure the wire link fitted between the 24 volt external connections is left in place.