My system had 3 sluggish radiators. I had one re-piped during some alterations. It turned out I had some sediment in the outlet union from the manifold. Perhaps flux type debris from the original build.
Unfortunately I was out when the plumber did the job so wasn't in a position to get the other unions checked. I now stil lhave 2 rads that are a bit sluggish.
I would like to run with a long term cleaner in the system. I always have an inhibitor and the water is very clean - I also have a magnetic think.
Any suggestions - is there something that I can use all through the winter without it attacking my boiler - but might clean any partial blockages (microbore of course)