Now draining the CH system after having Fernox Restorer running around
in it for a few days.

Filling and draining it until the water comes out is clear is
'interesting work' - running up and down stairs | loft ladder | opening
radiator bleed points | bleeding rad's...

How clear do I really need to get the water before it's clean enough?

--
dave @ stejonda
Bring culture back to NTL.
http://www.performance-channel.com/