"Andy Turnbull" no email please! wrote in message
...
Hello,

In a closed CH system where everything is new (boiler, pipes and
radiators)
is it possible to still get a build up of sludge in your radiators and if
so
how?

Yes, if you don't put corrosion inhibitor in the water.
Probably happen faster if you don't flush out the acid residues from
soldering.
Even so, it should take some time for an appreciable build up of sludge.
If you bleed some water off from a radiator and it is black, then this
suggests corrosion and sludge.

HTH
Dave R