Ferroli Modena 80 Central heating boiler problem??? Please HELP!!?

I've got a Ferroli Modena 80 boiler which ramdonly switches the warm water (as if you started the central heating??) This only happens for about 30 seconds and then switch itself off but frequently happen every half hour, which is very annoying!!! I've switch the boiler off/on and also reset it, I've even look at the timer and even reset that so there's no timer programmed. But it still occurs!! Since this has started one of my radiator upstairs has started to make clicking sounds every time the boiler is goes on/off for 30 seconds. It's very annoying!! Please HELP! any info is very much appreciated.