Office Chair Keeps Sinking? How to Fix a Worn Gas Lift Cylinder

Why Does My Office Chair Keep Sinking?

If your chair slowly drops the moment you sit down — or won't stay at your set height at all — the cause is almost always the same: the gas lift cylinder (also called a gas spring or pneumatic cylinder) inside the base has lost pressure. It's the single most common office chair fault, and it happens to every chair eventually as the internal seal wears with repeated use.

The good news: it's a five-minute DIY fix, and you don't need to replace the whole chair.

How to Confirm It's the Gas Lift (Not Something Else)

Before ordering a replacement, rule out the alternatives with a quick check:

• Sits fine unweighted, sinks when you sit down — classic gas lift failure.
• Height lever does nothing at all — could be the lever mechanism rather than the cylinder itself.
• Chair leans or wobbles as well as sinking — check the base and castors aren't damaged separately.
• Hissing sound when adjusting height — confirms a gas leak in the cylinder.

If your chair sinks under weight but the lever otherwise works, the gas lift cylinder is the culprit in the vast majority of cases.

Is It Safe to Keep Using a Sinking Chair?

A chair that slowly sinks isn't usually dangerous, but a cylinder that's failing can occasionally drop suddenly rather than gradually, and long-term use at the wrong height contributes to back and posture problems. It's worth fixing sooner rather than later — especially for a chair in daily use.

How to Replace an Office Chair Gas Lift

1. Remove the seat from the base — most chairs simply pull off the top of the cylinder, or are held with 4 bolts underneath the seat pan.
2. Remove the cylinder from the star base — tip the base upside down and tap or lever the cylinder out (a rubber mallet or a pipe wrench with a cloth to protect the metal works well for stuck cylinders).
3. Measure your old cylinder — total length and diameter — or measure the gap in your base if the old one is missing.
4. Fit the new gas lift — push firmly into the base, then refit the seat mechanism on top.

Most standard office chairs use a universal-fit cylinder, but always check the diameter (28mm is the most common UK size) against your base before ordering.

Choosing the Right Replacement

Browse our Office Chair Gas Lifts collection for UK-stocked replacement cylinders in the standard lengths and diameters used across most home and office chairs. If you're unsure which size fits your chair, our team can help — just get in touch via the Contact page with your chair's make or a quick measurement.

FAQ

Why does my office chair keep going down when I sit on it?

The gas lift cylinder has lost internal pressure and can no longer support your weight at the set height — replacing the cylinder resolves it.

Can I fix a sinking office chair without replacing the whole cylinder?

No — gas lift cylinders are sealed units and can't be re-pressurised or repaired. Replacement is the only fix, but it's inexpensive and takes minutes.

What size gas lift cylinder do I need?

Measure the total length of your existing cylinder and its diameter where it inserts into the base. Most chairs use a 28mm diameter cylinder in a range of standard lengths.

Same-Day Dispatch

Orders placed Monday to Sunday before 16:00 are dispatched the same day via Royal Mail or Evri, so a sinking chair doesn't have to stay broken for long.