Can a magnet of a heating pipe really stop it clogging up?

[kilkenny]

Have seen adverts for magnets that stop your heating pipes from scaling up. Also they breakdown limescale. A friend is having a new heating system installed and engineer wants to fit one (for an extra �160 of course)

Have seen lots of websites in this regard but none have any scientific proof.

Comments welcome!!!!!!!!!!!!!!!

[buildersmate]

They don't stop limescale but there would be no limescale to keep reforming in a CH system - because the water in the system is sealed and doesn't keep being refreshed.
They do stop black sludge (magnetite) collecting in the bottom of the rads, preventing proper flow of hot water. I believe them to be a worthwhile addition to a new CH system and have one to my own system. They cost about �80 for the basic unit. Every now and again, one removes them and wash the sludge away - being magnetic, magnetite sludge sticks to the core magnet.
Please note this gadget is NOT the same thing as magnets folks try and sell you to go on the cold water pipe to remove scale. These do not work well.