Why is my boiler not working?

our BAXI boiler keeps being fixed momentarily. the heating will come on for an hour or so then just go again untill fixed. The hot water works 50% of the time though. The light and flame on the boiler isnt on. the pipes by the tank are cold. i can see switches around the tank but i dont know what they do . The first guy to look at it is a plumber and couldnt see anything wrong . he managed to get it working but i dont know how. yet it stopped after an hour. the second guy isnt a plumber but also got it working for an hour. Is there something i can try?