Ariston EuroCombi confusion ?

Hi

I have recently moved into a property that has an Ariston EuroCombi. I am not familiar with this boiler, so have downloaded a User Manual, and read through the entire thing. I have reprogrammed the timer, so allow the heating to come on according to my schedule etc. The problem is, this boiler seems to be constantly trying to ignite ... all day long, it clicks away as if it wants to ignite itself, but never really gets there. The central heating works fine, and the boiler seems to be quiet (no continuous attempts at ignition) but once the central heating is off, the thing just cracks on and tries to ignite until the timer kicks it into gear!

Any ideas?