Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove the wire from the "RT" terminal on connector X1 and make safe
Fit a wire link between "L" and "RT" terminals on connector X1
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the 240V external controls bypassed does the
boiler respond to a CH demand?
Note.
If boiler still does not respond leave external controls linked out until a diagnosis is reached.