What is wrong with my vokera boiler?

I`ve had 3 plumbers out and none of them no what the problem is, I have a vokera condenser boiler and when I put heating on the red light comes on and totally switches the heating and hot water off, Have to turn the dial to reset it again and it does same thing again. Its only 4 years old, It gets surviced every year. Is there anyone that can help at my wits end!!!