A major factor to consider when purchasing a new boiler is how long it will take to pay for itself. If you are replacing an old energy-inefficient one, you will save some money on your gas bills. But the amount you will save depends on how inefficient your boiler is. The costs of replacing and installing a new boiler will be outweighed by the savings you will make over the years.
If you are upgrading an old gas boiler without controls with a new A-rated condensing boiler with a programmer, room thermostat and thermostatic radiator controls, the table below explains how much you could save: