How can I fix my valiant boiler?

Our boiler is a few years old but the last couple of years we have had a problem with it cutting out and a red light showing on the boiler where there is a pilot light sign. It used to be in winter when the heating was on as well as running the hot taps but now it is going off all the time without the heating being off. We have to keep going and restarting the boiler to get it working again. We have had a new circuit board fitted last year but this obviously wasn't the problem.