Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Place a wire link between terminals 1 (brown) and 2 (black) of the main terminal strip labelled "Room thermostat / timer"
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now fire on a heating demand ?