NordicTrack treadmills are typically reliable and well constructed, but some problems can always develop. Problems with the speed of your machine usually are the result of a few specific problems that you can fix yourself, though you may need to order some new parts. Unless your treadmill is brand new, and therefore likely to be under warranty, compare the cost and value of purchasing a new machine before buying parts for your current machine.
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Worn Walking Belt
The walking belt of any treadmill will eventually wear out. Since the walking belt must be smooth and in good condition for the treadmill to operate properly, you should replace a walking belt that shows tears, holes or fraying edges. NordicTrack has a toll-free number you can call listed on its service website to order new parts and ask questions.
A walking belt that has been tightened more than necessary will move slower than it should. You can fix this problem easily by using the hex key that came with your treadmill to loosen the idler roller bolts on the rear of the walking platform. To check if your belt is too tight, attempt to lift one side of the walking belt off the platform about halfway down the platform. If you can't pull the belt up three inches, the belt is on too tight.
Old Walking Platform
The walking platform may wear out just like a walking belt. Replacing the walking platform is a more complicated procedure than simply changing a belt. Basically, you must remove the endcap screws, the roller adjustment bolts and platform screws so that you can slide the walking platform out and put a new one in its place. Call NordicTrack for details on how your model's platform can be replaced or have them send a repair person to do it for you.
A malfunctioning display causes speed problems because the speed readings will be incorrect. This is likely because the reed switch and magnet under the hood have become too far apart. You can fix this problem by removing the hood and sliding the reed switch to within 1/8 inch or 3 mm from the magnet. Consult your manual on how to remove the hood and the number of screws holding it in place.
Without the use of an appropriate, functioning surge suppressor, the control system of your treadmill can be damaged, which may cause the walking belt to speed up, slow down or even stop completely. A monitoring light will illuminate when the surge suppressor is working properly. Purchasing a surge suppressor is easiest to do through NordicTrack as the company will know what type your treadmill needs.