Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Insert a wire link to bypass the external controls
(as indicated below by the red arrows)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now respond to a CH demand?
(Radiator symbol in display)
Note:
If the boiler still does not respond to a CH demand then leave link wire in position.