I have a baxi 105 HE with integral 7 day timer - but I cant set timer?

I reset the timer and when I come to programme, the numbers 1-7 keep flashing at the top and will not stop.
The only thing I appear to be able to change is the time, but that will not set the clock or move me onto the next stage.
I recently moved to this house and have all the instructions which I was following, but I seem to be frozen, and am currently having to use manual override for the heating.
I have set this once before and was just intending to adjust the times. Has anyone else had this problem and do you know how to overcome it.