So by your question and you only wanting relevant answers ,what are you after.
If you want to know the actuall savings in regards to possibly changing your boiler.
You will have to ask a far more in depth question .
As in what sort of system was in before what controls did it have on it was it a gravity system , was it fully pumped, what boiler was fitted ,where the rads changed for better output rads , has it been changed for a combi , is it used the same length of time .is the room stat set at same temp etc etc .
It is not just a straight forward question as in i now have a condensing boiler and i am saving this amount that will tell you very little on where the savings are actually being made