Is This Hiding in YOUR Radiators? "Magnetite Sludge" If your heating system is slow to warm up, or your radiators have cold spots at the bottom, This is the "magnetite" sludge that has just been pulled out of a system using the Powderflush method. Why a standard flush often fails: Standard power flushing uses water and chemicals to "rinse" the system. But as you can see, this sludge is thick, heavy, and stubborn. Water alone often just flows right over the top of it. The Powderflush Difference: