F20 error code???
Ok, I found 2 solutions for this problem, I tried the first one, and it really seemed to work, but I think I will do the second one too. First, if you have metal flood safe hoses, you need to look for debris blocking the filter at both ends. I kept checking the screens at the washer end and not seeing anything, but there was debris located at the water supply end, stuck in the flood safe device that is in the metal hose. Also, Flood safe hoses say to turn the water on to full pressure, but sometimes that can activate the flood safe device, so only turn your water supply on half way. Make sure that the hoses are on right as well, the flood safe device needs to be at the end with the water supply, not the washer end. You will be able to see the device (it looks like a little sieve) inside the hose.
Another cause of this problem can be the filter IN your washer, it is located in the front just under the front bottom removable panel. If you have a pet in the house, definitely check this out, a lot of hair gets stuck in that. Just unscrew the front bottom panel, and then it is right in the middle at the bottom, a cone shaped filter. Get a towel, because there will be water in there, too. Check out this link with pictures: http://enginerdandwife.com/2007/03/kenmore-elite-h3-washer-error-code-hf.html