Baxi 50/5 backboiler keeps turning off and not restarting?

Hi all,
Our 8 years old boiler has just started playing up,we noticed a prob the other morning after realising we had no hot water,I checked the boiler and the pilot light was out,after checking the thermostat,turning the timer to continuous I reset the boiler by turning the dial to off position then back on after a min and the boiler fired up? after running for 20 min it then shut itself down again? I then restarted it again and yes after a short while it turned it self off again?

I phoned my engineer who came out cleaned,serviced and checked the boiler then gave it a clean bill of health?in the last few days the boiler has worked intermittently its worked on 3 full timer settings(a couple of mornings and evenings) the other times its either not started or its started and then shut its self off?(I have seen 3 different colours from the neon light green,amber and red)reading the manual I'm obviously resetting the boiler each time is fails to work but why.......?


Any ideas? Please???

Thx Tony