Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove OpenTherm connections from 11 & 12 on X4 and make safe
Fit a wire link between connections 11 and 12 on X4
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now respond to CH demand?