If you have a tilt back (or ease back) chair and it no longer returns to the upright position, your gas strut has failed and needs to be replaced. This is a relatively simple operation as they are held in place with clips, though the outback of the chair will have to be removed for access.

If you order a part from your dealer and it arrives, DO NOT remove the safety clip from the strut until it is installed in the chair. If you do, the strut will over-expand and is likely to damage the internal seals and you will then have to buy another $ 50 strut. Resist the temptation to 'see if it works' ! Treat it like a hand grenade, its ready to go off if you pull the safety clip.