Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Disconnect an orange lead from the overheat thermostat
and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Turn on the boiler thermostat, the appliance will go to lockout.
Turn the boiler thermostat to OFF.
Isolate Mains Power to appliance as per TOP's P4

Reconnect orange lead to the overheat stat.
Mains Power On
Wait 10 seconds and turn boiler thermostat to calling position.
Does appliance start ignition sequence signifying lockout has reset?