Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Gain access to upper PCB behind the display
Remove X31 (programmer) connector from the PCB and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With X31 connector removed does the boiler respond to a CH demand?