Hi Yes you can alter the flue. i had the same problem. i put a conservatory on the back of my house and either had to move the boiler which was going to cost £700 or alter the flue. I got onto potterton who sent me a brochure with all of the flue options for that boiler. i then ordered the flue kit through jewsons which cost £150
Fitted it myself
Result
John
May 2007