In alphabetical order:
Bowflex - This is for the 3, 5 and 7 series of treadmills. Press and hold the ENTER and POWER keys for 3 seconds. This puts the treadmill into dormant mode. From here you can access many features, refer to your user manual for each one and how to access them.
For the BXT series turn on the treadmill and it enters the power up mode. While in this mode hold the pause/stop button and decrease button for 3 seconds to access the machine settings. From here you can make various choices by pressing up or down. One of the choices is a reset console. When highlighted, activate it by pressing enter.
For the Treadclimbers, turn on the machine to enter the power up mode. While in the mode hold the stop/pause button and right button for 3 seconds. As with the BXT series you're now in machine settings. From here you choose the reset console option and press enter.
Cybex - The on/off switch as at the front of the motor cover. Turning it on will place it in dormant mode. The set up menu can be obtained by pressing "Clear 750" on the keypad. Always contact customer service with any problems.
Freemotion - First get to the settings mode by accessing the start up menu. Touch the "i" button near the lower left corner of the screen. From here you need to enter the maintenance mode by pressing the maintenance button in the lower left corner again. Then you have all sorts of functions you can perform including the factory defaults by pressing the selection where it's shown.
Horizon Fitness - Press the stop button to ensure nothing is running on the machine. When everything has stopped press and hold the stop key for 3 seconds and this will perform a reset.
Life Fitness - On a lot of models there is a reset button. On most there is a diagnostics feature that requires some different codes for each model. The model and diagnostics code for Life Fitness treadmills can be found on that link, they differ for nearly every treadmill they make.
Matrix - There are two stages to do a reset. For a normal reset hold the PAUSE button down for 3 seconds. Next there are manager settings from which you have more access to the different preset options within the treadmill. Press and hold the ELEVATION DOWN and SPEED UP for 3 seconds. The speed up and down buttons will cycle through the different settings.
Nautilus - There is an in built diagnostic system you can access by pressing speed: UP, 6, ENTER. When in this mode you can test various components and parts of the treadmill. Check your manual to see which you can access and how to initiate them. When finished with diagnostics press the CLEAR key.
NordicTrack - Ensure the machine is not in a program or moving. Locate the reset hole/button underneath the console. This will require a Q-tip or such like to press the button. When done the treadmill will perform the reset.
Precor - There is an on/off switch below the hood near to the power cable. Ensure everything is stopped and at zero and turn off for 30 seconds and then back on. Some models will have a reset button. Others will need the programming mode which can be obtained by pressing RESET, 5, 6, 5, 1, 5, 6, 5.
Proform - These are made by the same company and has similar software and components of the NordicTrack treadmills above. So ensure the machine is not in a program or moving. Locate the reset hole/button underneath the console. This will require a Q-tip or such like to press the button. When done the treadmill will perform the reset.
Sole Fitness - Press the stop button to ensure nothing is running on the machine. When everything has stopped press and hold the stop key for 3 seconds and this will perform a reset.
Woodway - The Woodway Curve has a reset button on the console to the bottom right. Press to reset all the values of the other readings and then press again during set up indicated by the mode diamond to zero.
Xterra Fitness - Ensure everything is at a standstill and not moving. Press stop, and hold it down for 3 seconds, then a reset will occur.
Most treadmills just have a reset button or the back of the console will have the hole you can use. If this doesn't work the on/off button and/or unplugging of the unit will result in a reset being performed. Always keep an eye on the display as this is where you will be told if what you've done is successful.
Finally the owner's manual should tell you how to reset. If you can't find it or don't have the manual anymore then the manufacturers all upload their's to their website. So a quick search will usually find what you're looking for. Sometimes a quick phone call will get you results. They're always quick to help then you can get back to running.