britony combi?

my boiler keeps cutting out i took cover off looked in combustion chamber and noticed the ionisation electrode looks burnt out i also noticed a black mark on the spark electrode lead outside the combustion chamber i just altered the postition of the wire and voila the boiler lit up and kept on running this has happened before could either of these things cause the boiler to cut out the boiler is 12 years old so has nt got the fault indicator lights apart from the single red onr