The F28 error code indicates a communication problem between the central control and the motor control. This simply means the control boards are not talking to each other.
This can be a difficult and frustrating problem to diagnose even for a technician. The problem can be a bad central control or motor control or loose connections between the two. If you're comfortable and confident in your do-it-yourself abilities there are some things that you can try.
Before taking anything apart and checking connections the first thing I recommend doing is to run a diagnostic cycle. See the 1st image below for how to do this.
If the unit fails to enter diagnostic then most likely the central control has failed.
If the washer enters diagnostic but the F28 error happens then the next thing to try is to check that all of the connections at the motor and central control are tight.
I'd start at the motor control. See the 2nd image for how to access the motor control. Remember to unplug the washer first.
The 3rd image shows how to access the central control.
I hope this information helps resolve this problem but you can submit another question with any additional details for further assistance.