A method of burning off accumulated contaminants from heat sink media of a regenerative oxidizer having a plurality of segments containing media arranged around a central axis and a rotary valve which includes repeatedly rotating the rotary valve 180 degrees to alternatively direct waste gas through a first plurality of segments, direct the hot gas through a second plurality of segments and purge gas through a third segment to burn off the contaminants, then indexing the rotary valve one segment and repeating the burn-off process of all segments.