Jim G Wood Dale , IL January 02, 2016 Appliance: Whirlpool Gas Dryer WGD6400SB1 Whirlpool Dryer Wgd6400sb1: Heating only at beginning of cycle. How to replace Dryer Gas Valve Coil Kit. With it's age I figured it would be time to replace a number of parts related to the heating cycle. So I started with the thermistor and high limit replacement and then moved to the flame sensor and gas valve coils. This also was a great time to clean out the entire cabinet. Very important with lint buildup and gas flame nearby. Do-It-Yourself Rating: Repair Time Estimate: 1-2 hours