We have an old boiler that breaks all the time, so I went with cover from British Gas.
At first it was a good deal at about £12 a month, now it's about £17 a month which I'm not as happy about.
But, when they come out, the engineers are excellent, they really fix it quick, whereas in the past when we had independent engineers out they'd just say it's an old knackered boiler and needs replacing, they'd fix it but would faff about with different parts. British Gas just get on with it.
Downside of course is it's costing me about £200 a year but you get an annual check-up and service included, plus the cover if it breaks.