sime 80e ingition board [boiler control ]?

hi, I have a problem on my sime 80 e friendly boiler id number 0063as4782 cd number 8092955 ser number 3001722337,this is the blue box that plugs in to the side of the gas valve,the ingition pc board, it some times fails to switch in the gas vavle and the spark up, this then leaves the pump and fan running if i switch it off then on again it usually re starts ok, i think it is a relay or scr at fault i have checked the board for dry joints,i would like to repair this problem my self [ ex tiffy at ici] a new board is £78-00 if you know which parts are needed i can then sort it for my self.hope you can help bob roberts.email is r.roberts97@ntlworld.com