Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove the internal programmer / timer
Insert a wire link between terminals 1 and 2
(as indicated below by the red wire link)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the internal programmer / timer bypassed does
the boiler respond to a CH demand?