Look at the 2 pipes below:-
Does the one on the Left look familar? What about your shower head and the inside of your kettle?
The White Substance that we call Scale is actually insoluable compounds of Calcium and Magnesium. These are very effective Insulators, so all the heat that your boiler is producing is not getting out of the water into your house. In fact, the Scale doesn't just coat the inside of your pipes, it also coats the heating elements of your boiler and the heat exchanger inside your hot water tank. So the heat from your boiler doesn't even heat the water!
Ceramics are so good at resisting heat that they are used to line the insides of Pottery Kilns and the outsides of Spaceships.
These compounds don't stick to surfaces whilst the water is cold (how many white river beds have you seen lately?), but heat the water up and they will stick to any available surface.
A Federal Technology Alert from the U.S. Dept of Energy found that a scale deposit just 0.8mm thick would lead to an increased energy requirement of 10% for the same amount of heat on the outside of the pipe. If you have Scale at your Boiler, inside your Hot Water Tank and at your Radiators, how much energy are you wasting?
So what are you going to do about Scale?
There are 2 choices here - a) remove the compounds before they get into your water system or b) control them when they are in your pipes.