Last year, I had two quotes to fit a new boiler in a first floor flat I own. One plumber (Corgi registered) said I could have a combi but British Gas claimed that the diameter of the incoming pipe to the building was too small. As this is just a flat, I can't replace the main supply pipe but I have since learned that the fellow in the ground floor flat has a combi and it works fine. So, now I'm confused. Is it possible that a combi on the ground floor might work where one on the first floor might not? Forgive me if this is a stupid question, but as most of you know, I'm a complete novice when it comes to plumbing.