1. About the burner: pull the knob out and check it from the inside for a crack. If there is nothing wrong then the infinite switch for this burner has to be replaced.
2. About glass top: if it's chipped of at the edge and not very visible - just forget about it. New glass top will cost you about $400 - if you can do it yourself.
- The part number for the knob (black) is AP3030013
- The part number for the infinite switch (left front burner) is AP3672660
- The part number for the glass top (black) is AP3047022
Here are the break down diagrams for the Kitchen Aid cooktop Model KECD865HBL3