reply to am i going to do work myself or get gas safe fitter

Hazel thank you for replying to my initial question. You need to invite a Gas Safe engineer to your property to make an assessment of your existing gas carcase, normally a 22mm gas service is required (15mm will be to SMALL) to serve your new proposed boiler, but this depends on how many other gas appliance's you have and how far away from the gas meter all appliance's are and the route the gas service takes, they are other factors involved which I will not confuse you with. Once you have invited a Gas Safe engineer, he will carry out a gas pipe sizing exercise and the suitability of the new boiler location. My advice to you is invite at least two engineers so you can obtain comparative surveys and quotations!