Office Chair Keeps Sinking: Diagnose It, Then Repair or Replace

By Desk One Team | Published: 20 September 2026

An office chair that slowly sinks while you are sitting in it has almost always lost pressure in its pneumatic gas cylinder — a sealed part that sits between the seat mechanism and the star base — so the repair is usually a cylinder swap rather than a new chair, and you only replace the whole chair when the base is cracked, the tilt mechanism will no longer hold its lock, or the seat foam has compressed flat.

Sinking is the most common office chair complaint we hear, and it is also the most over-diagnosed. Plenty of structurally sound chairs get thrown out because one sealed component about the size of a torch has stopped holding pressure. This guide covers what that component does, the tests you can run at your own desk with no tools, what a replacement actually involves, and the three conditions that mean the chair genuinely is finished. It also tells you plainly where our own published specifications stop, because that matters if you are trying to source a matching part.

Key takeaways

• A gas cylinder is a sealed pressure vessel. It cannot be refilled, topped up or serviced — it is replaced as a whole unit, and no amount of lever adjustment will fix a leaking one.
• Run the empty-seat test first. Raise the seat to full height with nobody on it and walk away. If it drops on its own, the seal has gone completely. If it only drops under your weight, the seal is on the way out. Both point at the same part.
• Replace the chair rather than the cylinder if any one of three things is true: a crack anywhere in the base, a tilt mechanism that will not lock, or seat foam that stays dented after you stand up.
• Only 6 of the 53 chair models on our site publish a weight capacity, and every one of those 6 states 120kg. Working near or above a chair's rated capacity is the quickest way to shorten cylinder life.
• DeskOne chairs carry a 1-year warranty, and a genuine fault or quality issue falls under our full refund within 5 days path — so talk to us before you spend money on parts.

How a gas lift works, and how it fails

Inside the chrome tube under your seat is a cylinder charged with compressed gas (usually nitrogen) and divided by a piston. When you tap the lever, you open a small valve at the top of the cylinder, gas moves between chambers, and the seat rises or falls. Let the lever go and the valve shuts, trapping gas at a pressure high enough to hold your body weight against gravity.

That whole arrangement depends on seals. Seals are consumables: they harden, they wear against the piston rod, and they eventually let gas bleed past instead of holding it. Once that happens the cylinder cannot support load, and the symptom is exactly what you are experiencing — a seat that quietly gives way over minutes or seconds while everything else about the chair feels fine.

This is why sinking is rarely a "whole chair" problem. Every other part of an office chair fails mechanically and visibly. Castors crack or seize. A base splits and you can see the line. A tilt mechanism strips and the backrest flops. Foam flattens and you feel the board through it. The gas cylinder is the only component whose job is holding pressure, so it is the only component whose failure shows up as a chair that will not stay at the height you set.

Four checks you can do at your desk, no tools required

Work through these in order. They take a few minutes and they will almost always isolate the fault.

• The empty-seat test. Lift the seat to its highest position with no weight on it, then leave the room. Come back and look. A seat that has dropped by itself has a cylinder with nothing left in it.
• The tape-mark test. Stick a piece of masking tape on the chrome tube level with the bottom of the seat, then sit and work normally. Check the gap later. Slow, steady travel confirms a leak under load — the most common version of this fault, and the one people mistake for "the lever needs adjusting".
• The lever feel test. Tap the lever with no weight on the seat. A healthy chair rises firmly. If the lever feels dead and nothing moves in either direction, you either have a cylinder with no gas at all, or a lever linkage that has slipped out of position and is no longer reaching the valve. The linkage is worth a look before you buy anything.
• The wobble and lock test. With the chair loaded, rock gently side to side and try the tilt lock. Play at the base, a creak from the join, or a backrest that refuses to lock are separate problems from sinking, and they change the repair-or-replace answer considerably.

What a cylinder swap involves, and when it is worth doing

Mechanically, it is a short job for anyone reasonably handy. Turn the chair upside down. The cylinder is held into the base and into the seat mechanism by tapered friction fits, not threads — no bolts to undo, which surprises people. The cylinder is separated from the base by tapping the taper loose, and separated from the mechanism the same way. The new cylinder drops in, and your own body weight seats both tapers the first time you sit down. A rubber mallet and a pair of grips is the usual toolkit. Wear eye protection and never cut, drill or heat an old cylinder; it is still a pressure vessel even when it will not hold your weight.

The harder part is sourcing the right one. Cylinder diameter, tube length and travel all vary, and getting a close-but-wrong part means a chair that is permanently too tall or too short. Measure the old one before you buy, and be honest about how much you are spending relative to the chair. Our chair range runs from $75 to $990, which is a useful way to frame the decision: on a chair near the top of that range, such as the Prestige at $543, a cylinder swap is obviously worth doing. On a chair near the bottom, a part plus your afternoon can add up to most of a new chair.

A caution worth stating openly: none of our chair pages publish a gas-lift class or grade. Sixteen models mention that they have a gas lift, and not one of them lists a class. Seventeen mention castors, and none publish castor material or diameter. Base material appears on only 6 models. Those gaps are real, and they are a good reason to ask us for your specific model before ordering a part or specifying a chair for a fit-out, rather than assuming a class from the product photo.

When the chair is genuinely finished

There are three failures where replacing the cylinder is throwing good money after bad.

• A cracked base. Whether the base is nylon or steel, a crack is a structural failure carrying your full weight at ankle height, and cracks propagate. This one is not a repair, and it is not a "watch it for a while" either.
• A failed tilt mechanism. If the lock will not hold, the tension knob does nothing, or the mechanism has play in it, you are looking at the most expensive single component in the chair. On most chairs it is not economically replaceable.
• Worn seat foam. Press your palm into the seat and release. Foam that stays compressed has lost its ability to distribute pressure, which is the entire ergonomic point of the seat. New foam feel is not something a cylinder gives you back.

Our rule of thumb: one of these three and it is a judgement call based on the chair's price and age. Two or more and you buy a new chair. If you are at that point, it is worth reading what the ergonomic chair features actually do before you shop, so the replacement fixes the reason the old one failed rather than repeating it.

Weight rating, and why it drives cylinder life

Every time you sit, the cylinder seals take the load. Sit close to the chair's design limit and they take that load at the top of their working range, day after day, which is precisely the condition that ages seals fastest. It is the single most predictable cause of a chair that sinks well before you expected it to.

Here is what we can actually tell you from our own published data, and what we cannot:

• Weight capacity is published on 6 chair models, and all 6 state 120kg — including the Essential at $279, Comfort Leather at $327, Prime at $439, Prestige at $543, and the Luxura Elite at $519, currently out of stock.
• The remaining models in our chair range publish no capacity figure. That does not mean they are weak; it means the figure is not on the page, and we would rather say so than invent one. Ring us with the model you are looking at.
• Exactly seven models carry a BIFMA claim: Ergo Flex v2 ($109), Ergo Comfort ($129), Ergo Lite ($247), Ergo Pro ($290), Grid ($614), Ultra Flex ($636) and Ultra ($734). Some of those pages state "BIFMA Certified Components", which is a component-level claim and not the same thing as whole-chair certification — we keep that distinction because it matters. The other 46 models make no BIFMA claim at all.

If you are heavier than average, or buying for someone who is, that combination of facts should push you towards asking questions rather than reading spec tables. Start with our heavy-duty chair weight capacity guide, then call so we can check the specific model against how it will be used. For a shared or hot-desked chair, assume the heaviest likely user, not the average one.

If your chair is newly faulty, stop and talk to us

DeskOne chairs carry a 1-year warranty. If a chair you bought from us has started sinking and it is a genuine fault or quality issue, that sits under our full refund within 5 days path — so do not start pulling it apart or buying parts before you contact us. A change of mind is a different path with different terms: return within 7 days, a 30% restocking fee, and freight at your cost. The two are not interchangeable, and the difference is worth a phone call.

Our stock is held here in Australia rather than drop-shipped, across two warehouses, which means we can often look at the same model you have in front of you:

• Brisbane (showroom, and local pickup available) — Unit A4-142 Sherbrooke Rd, Willawong QLD 4110. 07 3879 0357 or 0466 787 593.
• Sydney — Unit 2, 11 Newton Rd, Wetherill Park NSW 2164. 02 9823 9703 or 0483 750 498.

If the outcome is a new chair, orders take 3-7 business days to process and dispatch, and you are welcome to browse the current ergonomic chair range first and then check the model with us. Our Judge.me store average is 4.79 stars, and a decent share of that comes from getting the specification question answered before the order rather than after it.

Why does my office chair keep sinking when I sit down?

Because the gas cylinder under the seat has lost the ability to hold pressure. Its internal seals have worn, so gas bleeds past the piston instead of supporting your weight, and the seat travels downwards. It is a component failure rather than an adjustment problem, which is why no amount of fiddling with the lever fixes it.

Can a gas lift cylinder be repaired or refilled?

No. It is a sealed pressure vessel with no service port, so it is replaced as a complete unit rather than repaired. Anyone offering to recharge one should be politely declined. Do not cut, drill or apply heat to an old cylinder either, even a completely flat one.

How do I tell whether it is the gas lift or the chair mechanism?

Sinking is the gas lift; almost everything else is not. If the seat will not stay at the height you set, that is the cylinder. If the height holds but the backrest will not lock, there is play at the base, or the chair rocks and creaks, you are looking at the tilt mechanism or the base instead. Try the empty-seat test to confirm: raise the seat with nothing on it and see whether it drops by itself.

Is it worth replacing the gas cylinder or should I just buy a new chair?

Replace the cylinder if the base is sound, the tilt mechanism still locks and the foam still springs back — that is a good chair with one dead part. Buy a new chair if two or more of those three have gone, or if the part plus your time is heading towards the price of the same chair new. Our chair range spans $75 to $990, so the honest answer depends a lot on where your chair sits in that spread.

Does sitting above the weight limit make a chair sink sooner?

Yes, that is one of the most reliable ways to shorten cylinder life, because the seals spend every working day at the top of their load range. Only 6 of our 53 chair models publish a weight capacity, and all 6 state 120kg. For the rest, the figure is not published, so ring us with the model rather than guessing from the photo.

Is a sinking chair covered by DeskOne's warranty?

DeskOne chairs carry a 1-year warranty, and a genuine fault or quality issue falls under our full refund within 5 days path. A change of mind is separate: a return within 7 days with a 30% restocking fee and freight paid by the customer. Contact the team with your order details before you buy parts or dismantle anything, because it is much easier to sort out while the chair is still intact.

Related guides

• Ergonomic office chair features explained, in plain English
• Choosing office chair castors for hard floors and carpet
• Heavy-duty office chairs and how to read weight capacity claims
• Is Desk One a reliable furniture store? What we publish and what we do not