Funnily enough I was just on to BG about their service like the one Harry mentions as the warranty on my boiler runs out in a few months, they charge £17 per month and for this you get 24 hour cover, up to 3 freecall outs, parts and labour per year and a yearly service of your boiler, so you'd get most of your money back with the cost of the yearly sevice at the prices certified gas fitters charge these days plus peace of mind knowing you're likely to find your self with a large unexpected bill