iron oxide deposits in pipes?

Can these deposits set hard in pipes? I have some in a section of piping in the ch system that I can't shift with X400 (in for a month) or flushing the system. Have been advised that it would be best to have offending section cut out by a plumber and replaced using compression fittings. The system is over 13 yrs old, and had not been drained before I did it 2 weeks ago. I know the deposits are there as a magnet sticks strongly to that section of pipe. It is in the airing cupboard where the feed pipe connects at the T piece to the horizontal section from the pump to the expansion pipe. Any advice welcome.