Hello, and thanks for requesting me. They tend to refer to Error 28 as a "speed control error code," so in order for me to troubleshoot and brainstorm, I need you to please answer me the following questions. Hopefully, we can get to the bottom of the issue. Feel free to give brief answers:
1) How long have you had the treadmill?
2) Has it been in storage or not used for a while, or you've been using it and the error just showed up?
3) Where exactly do you have it plugged in, and it is on a 15-20 Amp dedicated outlet/circuit?
4) Did the issue just start, or has it happened before?
5) Does the error happen after a workout, or even before you start it up and does no even run at all?
These will help tremendously.
I would suggest you go into service/diagnostics mode