Not mentioned in boiler instructions ?

I have a Baxi Combi 105HE Boiler. We do not have a thermostat connected to it so we just use the one on the boiler itself and also the integral timer.
We don't want the boiler on all the time and the wife, although been shown many times what to do, is reluctant to touch it incase she damages it.
After having it recently serviced, I decided to put an external timer and thermostat onto it The ones I have gone for are the Drayton LP111
timer and the Drayton RTS8 CombiStat.
Remove link from pin 1 & 2 on boiler
Connect pin 1 to timer LIVE and return switch wire to pin 2.
Neutral from timer to mains input neutral.
On the timer, LIVE from pin 2 of boiler to LIVE on timer with link to connection 1.
Neutral from boiler to neutral on timer.
Switch return from connection 3 on timer to pin 2 on boiler.
Now the big switch on. Timer lights up and desired heating on/off times installed.
Boiler did not start up at desired time. Manual override did not work, although timer indicated that it was.
Only when I switched the integral timer to constant did the external timer work as it should.
Is this right....? I thought the purpose of an external timer was to do away completely with the integral timer,
but there was nothing in the instuctions. Am I supposed to remove integral timer ?
Not fitted thermostat yet until I know everything is working correctly.
Oh by the way, timer switched boiler off at desired time.
Your thoughts and comments most welcomed
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You either need to remove the integral timer and link out the connections or leave it in the ON position.
The two timers are in series so you need both timers to call for heat to make the boiler fire up.
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