Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove the external controls wiring from terminals 1 and 2 at the incoming mains terminal strip and make safe
Fit a wire link between terminals 1 and 2
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the boiler now respond to the central heating demand?
Note:
1. If the boiler is not fitted with external controls and a wire link was already present leave this in place and select the first outcome below.
2. If a wire link has now been fitted but the boiler still does not respond leave wire link in place until a diagnosis is reached.