If you have thermostatically controlled heating in your home, and most of us do, then your boiler will be controlled by the temperature measured in a particular area in your home i.e. where the thermostat is placed! Regardless of how well insulated you home is the boiler will burn fuel and supply heat to your radiators until the temperature set on this thermostat is reached, before switching itself off. This does not mean that all of the rooms in the house are at the main thermostat temperature, their temperature will be dependent on the heat loss from the room, the radiator heat output of each room and the individual radiator thermostat (if you have them fitted). So the more you can do the reduce heat loss from your home the more rapidly the desired temperature will be reached and the earlier the boiler will switch off, ultimately reducing the amount of fuel you burn and amount you pay.