Differences between new and old condensing boilers:
Old condensing boilers use a different amount of useable heat they produce from the fuel it burns in comparison to new condensing boilers.
Old boilers usually have a pilot light, which is burning all the time, despite whether the boiler
Is switched on or not.
A condensing boiler is more efficient than a non-condensing boiler. It has a much larger heat exchanger, which extracts over 90% of the heat from the fuel it burns, making it much more cost effective to run.
It extracts the heat from the flue gases, which would otherwise be lost to the atmosphere, and recycles the heat back into the heating system.
The water vapour in the flue gases can be so cool that it condenses (hence the name!), and is taken away to a waste pipe through a condensate pipe.
Condensing boilers do not need a pilot light burning all the time, because they fire up when there is a demand for heat, suing an electric spark.