Fault on boiler Potterton Suprima 60?

A couple of weeks ago my Potterton Suprima 60 developed an itermittent fault after 4 years of perfect operation. Now the heating and water don't come on at all. You can hear the bolier trying to ignite all the time, occasionally it will come on but go off after a couple of minutes. I've tried using the reset button, but it doesn't do anything. What could be the problem?
Many thanks.