Almost always the gas cylinder: the seal inside it no longer holds pressure, so the seat drifts down under your weight. The cylinder is a replaceable part, and the rest of the chair is usually fine.
How to tell. Set the seat to a height and sit normally. If it creeps down over minutes or hours — or drops when you sit down hard — the cylinder is losing pressure. If the seat will not rise at all when you lift the lever with no weight on it, check first that the lever still presses the small button on top of the cylinder: a bent lever or a worn actuator can mimic a dead cylinder and costs far less to fix.
Why it happens. It is wear, not misuse. The seal works every time you sit or adjust the height, and after years it lets gas past. How long gas lift cylinders last covers what affects it.
Measure before ordering. Cylinders differ in overall length, in the travel they give, and in diameter. With the chair on its side, measure the exposed cylinder from the base to the seat mechanism at its lowest and highest settings, and note the outside diameter where it enters the base. A cylinder that is too long raises the lowest seat height; one that is too short leaves you too low at the top.
Replacing it. The cylinder is held by a taper fit in the base and in the seat mechanism, not by screws. The usual method is to tap the base off the cylinder with a rubber mallet and work the cylinder out of the mechanism, often with a pipe wrench; follow the cylinder maker’s instructions and wear eye protection. The new one pushes in and is seated by sitting on the chair.
When the base goes too. If the base is also cracked or the casters are worn, a complete kit can be simpler: the Topdeep in the chair casters and parts hub bundles a 28 in base, a cylinder with 5 in of travel, a seat plate and five casters for about $66.
Prices quoted in this text were read on 2026-10-13. The live price is at the top of the page.
Last reviewed 13 October 2026