I like soft water (softened with a unit that uses salt) but I hear that the salt ruins boilers aluminium heat exchangers. Since most boilers do have aluminium heat exchangers, I find it odd that the manufacturers (Permutit, Prismermetic, etc) do not mention this. As far as I can gather, only one boiler maker (Vaillant) actually has a cast iron heat exchanger anyway. Is this danger over-stated? Or would I be foolish to go for an ordinary boiler. I was thinking of a Worcester Bosch combi. Thank you.