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?