My washer was giving me the F21 error. The troubleshooting guide in the manual said it's got something to do with the drain pipe, filter or the pump.
After watching few videos online, I figured this is something I could do.
*****MAKE SURE THE WASHER IS UNPLUGGED BEFORE ACCESSING THE PARTS*****
You will only need just a couple of tools to tackle this project, but it's fairly easy to do for a handy person. Having a Wet Vac will be very helpful.