Cowboys, dont do a proper service
How much does it generally cost to calll someone out anyway? Maybe just put £10 a month into an account for this purpose. The amount of excess you'll pay will just depend on how much money is in it and you'll at least have a choice which person you use. After a year or so you'll pretty much have completely free breakdown cover too unless your boiler goes completely beserk.
All that good advice and STILL it gets heat. Some people just can't be told!
I only want it for a boiler service. Worth it for that?
Sub contractor, poorly vetted workforce, you may as well stick a pin in the Yellow Pages, hope for the best and expect the worst.