you can go wrong with any boiler including worcester bosch, they all have large service and warranty departments but thats ok as long as you are aware of this.
get to the library and read the WHICH mag for free, sept 08 and sept 07 , a report on boilers and servicing
this is from their users viewpoint, any advice you get from an installer will be swayed by how much money they can make
thats ok too as long as you realisle this
my advice is worcester bosch, valliant, glowworm, baxi potterton can all go wrong ,sometimes but you get what you pay for and they seem to be the ones that get recommended the most
so read the report and see what you think