I hired Billy based on the recommendations in this thread. He extended the flue on my boiler. It turned into a tough job because whoever installed the boiler ten years ago did a rubbish job fixing it to the wall and the boiler came loose when the flue was detached. Billy and his colleague remounted the boiler properly and completing the original job. He did not charge extra and the bill came within the range he gave as an estimate. Billy and his colleague were pleasant to deal with and tidied up after themselves. My only minor complaint is that he was very busy so it took a while to book him, which is probably a good sign. I will be hiring him next time I need work done.