Raymond R College Park , MD March 06, 2015 Appliance: Whirlpool Electric Cooktop RC8400XKW1 Whirlpool Cooktop Rc8400xkw1: Broken control knob needed replacing. How to replace Range Top Burner Control Knob. My Whirlpool electric cooktop is over 30 years old. I thought it would be difficult to find an exact match to the other 3 knobs - not so! It was easy, fast, and simple. I am VERY happy. Do-It-Yourself Rating: Repair Time Estimate: Less than 15 minutes