I've used a great plumber in the area - a young guy called Brian Nelson. I don't know that he does central heating installation, but it can't hurt to give him a call and ask - 4734845. *And* he cleans up after his work!
Recently used a company called Domestic Heating Ltd-they are on the Bord Gais approved list-had already spoken to two other "messers".
The chap that did the job was great and while not cheap did an excellent job and its guaranteed.