how can i fix my boiler that keeps cuttin out?

i took boiler out and it fired up
i turned it off and left for 5 mins and the when i went to turn it on again not a meg out of it

i left for an hour and then turned it on and fired up,

i attached the boiler again and seemed to be ok but then conked after 5 - 10 mins and now not a meg out of it again