Is your boiler energy efficient?
If it's 10-15 years old then it probably isn't. Replacing your old boiler with a new condensing boiler can save you around a third on your heating bills straight away.
Around 60% of CO2 emissions from your home are down to your boiler. With an efficient new boiler you could save up to 875kg of CO2 and £130 a year.
Add in a full set of heating controls as well as a new boiler, and you could increase the total savings to around £250 and 1.7 tonnes of CO2 a year.