Two radiators are getting sluggish. The last time I removed one for
decorating I checked the flow - There was a good flow out of the "return"
but a poor flow from the "flow" pipe.

The pipes are behind the plasterboard (wallpapered only last year) and in
the case of the other - the pipes run under a laminate floor. I am therefore
keen to try a cleaner - and was thinking that if I turn off all the other
radiators it should maximise the effect on the blocked pipes.

Any comments - any suggestions? Do all cleaners need to be thoroughly
flushed out? Are some better than others?. I have tried using mains water
pressure to improve the flow - without success.