My house is heated by an oil furnace which also heats our water. Recently our shower's hot water began to cycle to luke warm every 5-10 minutes - with the luke warm water lasting 5-10 minutes depending on if the heat was on at the time. We called a technician to clean the coils, which really increased our hot water temperature - but only for a week and the temperature was still cycling. We've always had an issue with hardwater (190 ppm or 11 grain) and we have to clean our shower heads often. We also have many drain problems with soap sludge for any drain that carries hot water. I would not be surprised if the the temperature cycling of our hot water was caused by pipes being caked with deposits - even inside of our radiator pipes, but I can't seem to find any methods online for descaling pipes. There are many sites for the magnetic or electromagnetic descalers - but I can't find a single study showing quantifiable results using this method.
My question is: what is the normal method of descaling pipes? Does a plumber replace every hot water pipe in the house? Can a chemical be cycled through the pipes/radiators that dissolves the scale?
Thanks.