If the walking belt has shifted to the left, use the Allen wrench to turn the left rear roller bolt clockwise 1/2 of a turn; if the walking belt has shifted to the right, turn the left rear roller bolt counterclockwise 1/2 of a turn. Be careful not to overtighten the walking belt. Plug in the power cord, insert the key, and run the treadmill for a few minutes. Repeat until the walking belt is centred.
Answers & Comments
Please see here for some Life fitness spares:
http://www.partsfortreadmill.com/catalogsearch/result/?q=Life+fitness
and here for dismantling your treadmill and changing the belt:
http://www.treadmillsrepair.co.uk/2013/12/belt-for-treadmill-replacement-and.html
If the walking belt has shifted to the left, use the Allen wrench to turn the left rear roller bolt clockwise 1/2 of a turn; if the walking belt has shifted to the right, turn the left rear roller bolt counterclockwise 1/2 of a turn. Be careful not to overtighten the walking belt. Plug in the power cord, insert the key, and run the treadmill for a few minutes. Repeat until the walking belt is centred.