As always, the answer is 'it depends'.
It depends:
whether you've got an old boiler that history tells you keeps breaking down
whether one is completely clueless when it comes to understanding where to get decent support from someone who isn't going to charge you the earth.
Simple laws of business ought to tell you that for all the people above who claim to have put less into paying for insurance than they've taken out, there are dozens of people who didn't bother to post an answer who just keep paying the premiums and don't get as much back - otherwise the insurer would be out of business.
I'm firmly with ridtipe on this. In about 30 years of having gas and then oil boilers, I've had to have a repair man out once - apart from for servicing the units. And even on that I only organise a service every two years and make sure I get the technician to tell about the condition of the boiler. It currently costs about £70 for a decent 45 minutes of service.
But, you pays your money, you gets your peace of mind.