My new Ferrolli boiler is playing up again?

I had a new Ferolli boiler fitted a few months ago and the engineer has been back 12 times at least, I posted on here not long ago and he has been back 4 times since then!, i had a problem with the heating not coming on when programmed, he fitted a new programmer after the 8th visit but its still not working properly, it came on at 4am this morning and didn't go off at the usual time, I had to turn it off, this boiler/thermo has a mind of its own and after 12 visits I think its fair to say that I want my money back or a new boiler fitting and NOT a ferrolli, the visits have cost me money as i have had to cancel work assignments because of this, I have had to have the original engineer back everytime because i am told that if it isn't a boiler fault then i have to pay!!!!!!! what ...under gaurantee?? does anyone know what I can do before i explode please, i have been very patient as I am now on visit 13!