"Christian McArdle" wrote in message
. net...
heating system. I'm thinking that if I desludge the whole system,
then the secondary heat exhanger will get desludged in the process
(apart from the channels that the mains water flows through, of
course, which is probably clear anyway. Anyone agree?

I would have thought that it was precisely the mains water flow channels
that are the problem. The CH side should have inhibitor in it and the
calcium will have settled out long ago. The mains side has fresh calcium
rich hot water, just ripe for depositing limescale.

After 3 years the primary sealed side would need another dose of inhibitor.