On Sat, 27 Jan 2007 10:25:39 GMT, Siggy
wrote:

I wish to do a thorough descaling and de-sludging of my sealed CH
system, and have bought a large tub of Fernox DS40 to accomplish this (I
hope).

I note on the instructions that it says to allow 7 days for it to work
on all-steel systems, but only 4 *hours* for those containing aluminium
rads.

So take it back and get something designed for aluminium ones that may
also work on steel?

There must be something designed to do this. You can't be the first to
have this problem.