Call me old fashioned but deffo old,extended boiler warranties are a fairly newish thing and are often used to sell boilers,the likes of BG hate them as they lose business and cannot compete.
Dont know the warranty conditions but i would be more in favour of a warranty if you can call your own installer to do the periodic inspection's and any repairs,your installer will understand your system and will be a very good person to have on speed dial to do any other work around your property.
Again being old fashioned,i have found many insurance type business's happy to alter their terms&conditions to work in their favour,so a warranty in year 10 could be very different than year 1.
Is wear&tear included in the warranty,for example your boiler needs a fan in year 6 is this covered ?
Plase dont think i am against extended warranties,just had the AA pay for a new power steering pump on a vauxhall (well they paid some,not all).
Good luck,
Erm, thanks?