Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Link out the external controls (and make safe)
(Terminals 5 and 6 at the boiler terminal strip)
Ensure appliance is set to WINTER mode - NO sun symbol in display
(Press reset button briefly to toggle sun symbol on and off)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan purge to complete (2 minutes).
Does the boiler now recognise and respond to the
central heating demand?
Note:
If boiler still does not recognise demand, leave the link in place until diagnosis is complete.