Why are my radiators cold at the bottom?

Black sludge is caused by corrosion inside steel radiators and pipes. It's more common in older systems without corrosion inhibitor.

A power flush can remove sludge from your entire system. For individual radiators, removal and flushing may be sufficient.

Adding corrosion inhibitor when your system is serviced prevents future sludge buildup. Have your technician check inhibitor levels annually.