How to Fix an Office Chair That Slowly Sinks

On this page (10 sections)

1. How do you know the cylinder is the problem?
2. Why do office chair cylinders sink over time?
3. What tools do you need to swap the cylinder?
4. How do you remove the old cylinder?
5. How do you fit the new cylinder?
6. Which replacement cylinder should you buy?
7. How do you reattach the base and check the fix?
8. What other chair fixes are worth doing at the same time?
9. When should you replace the chair instead?
10. How to fix an office chair that slowly sinks: the short version

To fix an office chair that slowly sinks, replace the gas lift cylinder. The seal inside it wears out, so it can no longer hold air pressure and the seat creeps down under your weight.

The good news is that the cylinder is the only part you need to swap. A Class 4 replacement costs far less than a new chair and takes about half an hour once you have the old one out.

How do you know the cylinder is the problem?

A seat that drops slowly while you sit is the classic sign of a failing cylinder. The height lever still works in both directions, but the chair won't hold where you set it.

Check the simple things first. If the lever sticks or the seat won't rise at all, the actuator or the lever linkage may be the issue rather than the gas lift itself.

Sit down and watch the height. A steady creep of an inch or more over a few minutes points to a worn seal inside the cylinder, which is the part that has to go.

Why do office chair cylinders sink over time?

Inside the cylinder, compressed gas pushes against oil to hold the seat up. The seal that keeps that gas in place wears with every adjustment and every sit.

Once the seal weakens, gas escapes slowly and the piston slides down under load. The Office Oasis says its cylinders are all Class 4, which is the highest durability rating for chair parts.

What does Class 4 mean on a gas lift?

Class 4 is the highest durability rating for chair cylinders. The Office Oasis says its cylinders support up to 1000 lb.

A higher class means a thicker tube and better seals, so the cylinder holds pressure longer. That's the single spec worth checking when you buy a replacement.

What tools do you need to swap the cylinder?

You need a hammer or mallet, a pipe wrench, and something to protect the base. A cylinder removal tool makes the job much easier if you don't already own one.

Lay down a towel so the base doesn't scratch the floor. Work in a clear space where you can flip the chair over and grip the base.

Some kits include gloves and step-by-step instructions. If yours doesn't include a removal tool, a pipe wrench wrapped in cloth usually frees a stuck cylinder.

How do you remove the old cylinder?

Flip the chair, pull the base off the column, then drive the cylinder out of the seat plate. Keep the base level so the column slides straight.

1. Turn the chair upside down and press the height lever to drop the seat to its lowest point.
2. Grip the base and pull it away from the column; it should lift off in one piece.
3. Set the base on the floor and knock the old cylinder out of its center hole.
4. Lift the seat mechanism off the top of the cylinder.

Some cylinders sit tightly in the base after years of use. A few firm taps with a mallet around the center hole usually break the grip.

A tall cylinder like the MASTERY MART, which runs to 17.2 inches fully extended, gives you more shaft to grip when it's time to pull it free.

Why a removal tool is worth having

The Office Oasis kit includes a purpose-built removal tool. The brand says it invented the first cylinder replacement kit with one in 2016.

That tool clamps the cylinder so you can twist and pull it out without damaging the base. It saves the wrestling match that comes with improvised tools.

If the base socket is scored or cracked from a past removal, check it before you press in the new part.

How do you fit the new cylinder?

Seat the new cylinder in the base first, then lower the chair mechanism onto the top. Push down until both ends are fully engaged.

Check the size before you start. The piston shaft should measure 1-1/8 inch (28 mm) across, and the column that sits in the base should measure 2 inch (50 mm).

Wipe any grit out of the base socket first. A clean seat means the cylinder sits straight and the chair won't lean or wobble later.

A column that feels loose in the hole is a fit problem, not a cylinder fault, so stop and remeasure before you sit.

Which replacement cylinder should you buy?

The right cylinder matches your chair's measurements and your seat height range. All three picks below use the standard 28 mm shaft and 50 mm column.

The Office Oasis cylinder is the pick for most people. It's a Class 4 lift rated to 1000 lb, and the kit ships with the removal tool, gloves and installation instructions.

Its 4.75 inch extended length covers standard desk chairs.

The brand backs it with a lifetime warranty and says it fits almost every office chair on the market, including the Herman Miller Aeron. If the fit is wrong, the brand offers to take care of it.

Pick the Rythalix cylinder if you want a height-matched size. Its 3.9 inch travel range suits seat heights from 5'3" to 5'11", and it fits top-activated chairs with the standard 28 mm shaft.

It won't fit side-activated chairs, including the Steelcase Leap series and the Aeron Remastered from 2013 on. Check your chair's lever position before ordering.

The brand describes the lift as running under 25 dB in use and as having an explosion-proof design.

Choose the MASTERY MART cylinder if your chair needs extra height. Its 5.5 inch stroke runs from about 11.7 inches compressed to 17.2 inches fully extended.

It's a Class 4, BIFMA-certified lift with a 1000 lb capacity. It fits the standard sizes and works with the Herman Miller Aeron, but not with IKEA chairs.

Measure the outer cylinder on your old part before you buy.

How do you reattach the base and check the fix?

Slide the base back onto the column, set the chair upright, and test the height at every notch. Sit down and bounce gently to confirm it holds.

Press the lever through its full range. The seat should rise smoothly and stop where you release it, with no slow creep under your weight.

If the chair still sinks, the new cylinder may not be fully seated. Flip it back over and press each end firmly into place.

A cylinder that only creeps when you lean to one side is usually sitting slightly crooked, so pull the base and reset it straight.

What other chair fixes are worth doing at the same time?

While the chair is upside down, check the base, wheels and arm bolts. One session under the seat saves you taking everything apart again later.

A base that rocks usually needs a look at the center hub; our guide on how to fix a wobbly office chair covers the causes. If the seat tips you forward, the office chair leaning forward fix explains the mechanism adjustment.

Worn casters roll badly and mark floors, so it's a good moment to learn how to replace office chair wheels. And once everything is back together, a session on how to clean an office chair gets the fabric or mesh fresh again.

When should you replace the chair instead?

Replace the whole chair when the frame, seat plate or mechanism is cracked. A cylinder swap fixes sinking, but it can't repair a bent structure.

A chair with a broken backrest mount or a mechanism that no longer locks needs a bigger fix than a gas lift. At that point, the cost of parts adds up quickly.

For most sinking chairs, though, the cylinder is the only worn part. Fixing it keeps a chair you already like out of the landfill and back under your desk.

A worn cylinder that also wobbles as it turns is still a cylinder job, since the swivel lives in the same part.

How to fix an office chair that slowly sinks: the short version

The fix for a chair that loses height is a new Class 4 gas cylinder, and the standard 28 mm shaft by 50 mm column size fits most chairs. Pick the Office Oasis kit if you want the removal tool included.

Choose the Rythalix for a height-matched top-activated chair, or the MASTERY MART if you need the higher 5.5 inch stroke. Measure your old cylinder first, then work through removal, fitting and a quick sit test.

With the new cylinder seated, the height holds and the chair feels like new. From there, keep the base, wheels and fabric in shape with the linked repair and cleaning guides.

Frequently asked questions

Why does my office chair slowly sink?

The gas cylinder has lost its internal pressure. A worn seal lets the compressed gas leak past the piston, so the seat drops a little at a time whenever you sit down.

A new cylinder is the fix.

Can I repair the cylinder instead of replacing it?

No. Gas cylinders are sealed units built to be thrown away, not opened.

Refitting a new Class 4 cylinder costs less than a new chair and takes about half an hour with the right removal tool.

How do I know which cylinder size to buy?

Measure the old one. The piston shaft that meets the chair is usually 1-1/8 inch (28 mm) across, and the column that sits in the base is 2 inch (50 mm).

Most chairs use these sizes.

Do I need a special tool to remove the old cylinder?

A pipe wrench or a few sharp hammer taps on the base can work, but a purpose-built removal tool is far easier. Some kits include one, which saves you from buying it separately.

Is it safe to keep using a sinking chair?

A chair that drops a little is annoying but not dangerous. If the seat falls suddenly or the cylinder hisses and wobbles, stop using it and replace the cylinder before you sit on it again.