A UK homeowner cleaned one of 10 radiators after some were not heating properly, then asked whether debris elsewhere in the system could circulate back. Commenters said it could; the homeowner plans to add X400 cleaner, leave it for weeks, then flush the system.
Commenters recommended flushing the heating system as a whole rather than draining radiators individually, and suggested a magnetic filter on the boiler return plus inhibitor after the flush. They also cautioned that black water alone does not show a radiator has been cleaned effectively.
