Shomari T Olathe , KS September 22, 2017 Appliance: Whirlpool Washer WFW8400TB01 Whirlpool Washer Wfw8400tb01: F20 error code. How to replace Drive Belt. Replaced the water inlet valve and the washer works flawlessly now. 19 People found this story helpful Do-It-Yourself Rating: Repair Time Estimate: 30-60 minutes