Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
(I regret that I am not able to offer Live Phone Call service at this time; However, your request is still open to other Experts in this category, and one of them may pick up on it at any time.)
There may be various problems with the incline, or its controls, or its mechanism.
The mechanism might be jammed.
Or the control circuitry might be defective. Or a sensor might be out of adjustment, perhaps.
How old is the treadmill in question?
And how long has the problem been going on? have you tried shutting the machine Off for several hours, even once, since the problem happened?
I regret that my suggestions and analysis cannot help. I have Opted Out, opening the main case (as well as the Live Phone Call request) to other Experts in this category.