My Ferroli boiler works as & when it feels like?

How do I work my Ferroli boiler? I've just moved into a house that has one. I switch it on & nothing happens. The clock thingy is completely blank and even when you re-set the re-set knob it still doesnt come on. The water comes on fine but it is the central heating part that I am having a promblem with. Some times if you leave the boiler on it for awhile suddenly the clock will suddenly display a time on it & then when I play around with the time buttons the heating will finally come on & I havent a clue how it does this. Thing is when I switch the boiler (as I do not know how to time the damn thing) I have to go through all this again. Please Help Me as the winter months will be here before I know it.
Thanks for reading