A Hydroflow HS38 clips onto the cold water pipe for the whole house and (from my understanding) sends an electrical pulse down the pipelines, clearing the limescale and preventing it sticking to the pipes. I was pretty sceptical when I first had one installed in my home, but the limescale was so bad I was willing to try anything (we had gone through 3 washing machines in 5 years!). Anyway I've had it about 18 months now and I've had no problems since, so it must be doing something right! I only just remembered when my client asked about limescale the other day - until then I'd kind of forgotten about it. You can ask your plumbing merchant for details and they should be able to supply and fit it for you if need be. The website is www.hydropath.co.uk
Pete
July 2010