Treadmill: Heart rate sensor isn't accurate
For the most accurate readings, hold your thumb over the heart rate monitor for at least 15 seconds while standing still on the foot rails. Don't press too hard or the circulation in your thumb will be restricted and it won't detect your heart rate. If your heart rate appears too high or too low or if you heart rate is not displayed, lift your thumb for a few seconds and then reposition your thumb on the heart rate monitor. The heart rate sensor is not a medical device. The heart rate monitor is intended only has an exercise aid in determining heart rate trends in general.
These repairs may help solve your Treadmill problem:
Replace the console display
The console displays the elapsed time, distance traveled, estimated calories burned, current speed, and the user’s pulse. If the console doesn't work, replace the console display assembly.
Replace the motor control board
The electronic motor control board controls and monitors the speed. If the motor controller is defective, replace the motor controller.