F28 means poor communication between the main control board and the motor control board.
Why it happens
- Improperly wired ground switches or reversed polarity.
- Damaged cable, which connects the two units.
How to solve it
- Unplug the machine.
- Check the RFI filter and the white wire, which leads to it. It should be toward the front of the machine.
- Check polarity on the outlet. When checking the machine for polarity, use a volt meter to ensure that white to cabinet ground is 0 volts.
- Make sure that the ground switches on the bottom and rear panels are closed properly.
If the switches are all right, most likely, the main control board has failed and needs to be replaced.