Microbore heating systems will have a multi connection manifold ,on a conventional system usually sited in the airing cupboard, or sometimes under the floorboards, each Rad is fed off this, and this is where mostly the sludge would build, in the past the the best way was to cut it out, either take it outside and clean , or buy a new one.when refitting be careful not to get your connections mixed up, best to call a Plumber first.
This is certainly not the case with a Wimpey Homes installation, there are no manifolds , they just reduce down pipe work sizing near to radiator .
Lesson I have learnt, on no account buy a WimpeyHome , let's face it they never even made a good Hamburger