When I serviced the pump assembly a couple of months ago, I had to chip off a huge amount of limescale, which was largely the cause of recurring blockages. But how do you de-scale the pipes? Would a few jugfuls of hot vinegar be any use?
Incidentally, I managed to clear the pipe blockage (which was particularly stubborn) by mechanical means in the end. I had bought some stuff called "Knock Out" which is concentrated sulphuric acid in case I was forced to consider using it. In the end I poured a very small amount down, after clearing the blockage, thinking it might gently remove a bit of the limescale. Having seen the reaction and heat produced as well as the possibility of spillage or splashing and serious burns, I really would NOT recommend fiddling around with this stuff. In fact, it is such a dangerous substance, I'm very surprised it's sold to the general public. I'm taking the rest to be disposed of - it's not something I really want hanging around at home.
Simon.