Since fitting the new boiler and controls, her fuel bills have gone now an incredible %! Sign up online or over the phone. Wondering about how energy efficient your new boiler will really be? Buying and installing a stairlift. Talk to us today about any boiler installation or repair questions you may have. What's the cost of replacing your boiler? In combustion processes, such as the combustion of gas in a boiler, the oxygen from the air reacts with the hydrogen from the fuel hot.