"F20" is called a No Water Detect error code. The following link explains:
This error code can be a tricky one to diagnose as there are several causes. In your case, however, you obviously don't have a water problem, or a drain problem. I think the problem is your pressure switch. The pressure switch is what shuts off the water source at the appropriate level. If it malfunctions, the washer will continue to fill to the point of overfilling. You should never have water above the glass as you described.
You can access the pressure switch by removing the top panel of the washer. The top panel comes off by removing the three screws holding it in place in the rear of the washer. With the screws removed, the panel will slide back, then lift off. The pressure switch will be located in the rear on the right hand side (as viewed from the front) along the interior cabinet wall. It is round, has some electrical connections and should also have a small plastic air hose attached to it.
Before assuming the pressure switch to be defective, trace the air hose to the bottom of the wash tub and ensure it is still connected. This hose is how the pressure switch detects the water level through pressure change in the tub as the water fills. If the air hose is disconnected or clogged, you can experience the same symptoms. You will need to remove the lower kick panel directly below the door inorder to see the bottom of the wash tub. Remove the panel by locating the screws under the bottom front edge. With the screws removed, the panel will drop down, then come off. The pressure switch air hose will attach to the lower right hand side of the wash tub.
If the air hose is attached at the wash tub, carefully disconnect it from the pressure switch and blow air through it. You should hear air bubbling through the residual water in the wash tub if it is not clogged. If it is clogged, carefully remove it and clean.
After verifying the air hose, you will need to refer to the troubleshooting index of your tech sheet for tips on how to properly troubleshoot and/or adjust the pressure switch. The tech sheet is located inside the washer behind the lower kick panel, or affixed to the inside of one of the interior cabinet walls. I do not have the pin numbers or measurements memorized. If the switch proves bad, replace it. If the switch is good, it may be the Central Control Unit (CCU). This is the main computer of the washer that controls all functions.
If you have any questions, or require additional assistance, please let me know. I hope you find this information helpful.