Office chair gas lift: Why your chair sinks and how to adjust it to feel like new again in 10 minutes

The gas lift (also called a gas spring) is the component in the centre of your office chair that adjusts the seat height continuously and provides the initial shock absorption when you sit down. If the chair slowly sinks while you are sitting on it, pressure loss in the cylinder is almost always the cause – a clear case for replacement. When buying a replacement gas lift, three values matter: the standard cone (usually 50 mm at the bottom, 28 mm at the top), the correct housing length/stroke height and the safety class according to DIN 4550 (Class 3 or 4 for continuous use).

A sinking office chair is no reason to throw it away. In most cases, the problem comes down to a single replaceable component – and replacing it only takes a few minutes if you know what to look for.

Office chair sinking? Typical symptoms & causes of a faulty gas lift

The symptoms are almost always the same, whether it is an executive chair in the office or a gaming chair in your home office:

• The chair slowly sinks while you are sitting, even though the height was set correctly beforehand

• The height adjustment lever can no longer lock properly – the chair drops down again immediately

• A quiet hissing sound can be heard as it sinks

• The chair can no longer be adjusted in height at all (permanently stuck at the very bottom or the very top)

The technical reason behind this: Inside the gas lift there is a piston rod in a cylinder filled with pressurised nitrogen gas. A small valve controls whether gas flows between the two chambers – this makes height adjustment possible. After years of daily use, the internal seals wear out, separating the pressure chambers from each other. As a result, gas continuously escapes, the counterpressure drops, and body weight slowly pushes the piston downwards – the chair "sinks".

A second, less common cause is a damaged or bent piston rod, usually due to improper strain (e.g. tilting sideways under heavy weight).

Why replacement is almost always worth it: A replacement gas lift costs only a fraction of a new office chair. The frame, backrest, upholstery, castors and armrests are usually completely intact – only that one mechanical wearing part in the centre has given out. Replacing it rarely takes more than ten minutes even without prior experience and requires no special tools.

Quality & safety classes for gas lifts (DIN 4550)

Not every gas lift is suitable for continuous office use. The European standard DIN 4550 (Part 3) classifies gas springs according to their tested load capacity and safety – identifiable by the GS mark ("Tested Safety"). Cheap, uncertified gas lifts from direct Far East imports often skip this test, which in the worst case can lead to a sudden loss of pressure or even the piston rod shooting out.

Rule of thumb for making your choice: For a classic office chair in normal 8-hour use, a Class 3 gas lift is perfectly sufficient. If the chair is used in shift work, as a 24-hour chair in a control room, or by users with above-average body weight, you should definitely choose Class 4 – the extra cost is minimal, while the safety benefit is considerable.

Finding the right dimensions: measuring the shaft, housing & stroke height

Before ordering a replacement gas lift, three dimensions determine whether it will fit properly.

The standard taper: 50 mm at the bottom, 28 mm at the top

Almost all modern office chairs follow a standardised taper size:

• Bottom (base): 50 mm taper – this fitting is virtually an industry-wide standard

• Top (seat mechanism): 28 mm taper – likewise the usual standard size for most branded mechanisms

These dimensions can be measured directly on the old gas lift after removal using a vernier caliper. Deviations mainly occur with very old or very inexpensive special models – if in doubt: remove it and measure first, then order.

Measuring housing length & stroke height

The housing length describes the installation length of the gas lift in the compressed state, while the stroke height is the additional upward adjustment range. Together, they make up the complete seat height range:

• Measure the old gas lift from cone to cone in the compressed (shortest) position

• Also note how far it can extend to its maximum (stroke height, usually 100–120 mm)

• Particularly small or very tall users benefit from a longer or shorter gas lift than the standard version – a targeted replacement can be worthwhile even without a defect in order to shift the seat height range individually

Suspension travel: Why cushioning when sitting down matters

High-quality gas lifts feature integrated suspension travel: when sitting down, the first part of the impact is gently absorbed instead of being transferred undamped to the spine. Especially with frequent sitting down and standing up in everyday office life, this effect adds up – a gas lift without this cushioning noticeably leads to an uncomfortable "hard" landing more often.

Step-by-step guide: Replacing an office chair gas lift yourself

Replacement is straightforward and requires neither a workshop nor any prior experience.

Prepare the tools

• Rubber mallet (not a metal hammer, to avoid damaging plastic parts)

• Flat-jaw pipe pliers or large water pump pliers for counter-holding

• Penetrating oil / WD-40 if the gas lift is stuck or has started to rust

• Optional: an old blanket or cardboard as a protective base

1. Turn the chair upside down

Place the office chair upside down on a stable, scratch-resistant surface so that the base is facing upward and the gas lift is easily accessible.

2. Remove the base from the old gas lift

The 50 mm cone usually sits very tightly in the base. With light, even blows from the rubber mallet against the side of the base (not against the gas lift itself), the push-fit connection will come loose. If the connection is particularly tight, a little penetrating oil can help if left to work overnight.

3. Remove the gas lift from the seat mechanism

Once the base is free, the gas lift can usually also be pulled out of the 28 mm cone of the seat mechanism by hand or with light tapping. For very tight connections, flat-jaw pipe pliers can help as a counter-holder.

4. Fit the new gas spring

The new, suitable gas lift is installed in the reverse order:

• Insert the new gas lift vertically into the base with the 50 mm end and press it firmly and straight until it locks into place

• Fit the seat mechanism with the 28 mm taper onto the top

• Place the chair back on its castors – the connection locks automatically the first time you sit down thanks to your body weight, so no additional screwing is required

After this final step, the chair is immediately ready for use again and the height can be adjusted continuously.

Conclusion & buying guide: Finding the right replacement gas lift

A sinking office chair almost never means the end of its service life – in most cases, replacing the gas lift is all it takes. Before buying, there are three key criteria:

• Taper dimensions: Usually 50 mm at the bottom / 28 mm at the top; measure the old gas lift to check

• Body length & stroke height: These determine the right seat height range for your body height

• Safety class according to DIN 4550: Class 3 for normal office use, Class 4 for continuous and heavy-duty use with GS mark

In the spare parts range at hjh-office.co.uk you will find certified gas lifts to DIN 4550 in chrome and black versions, with different body lengths and stroke heights – suitable for common standard tapers as well as many brand-specific special sizes. This means your office chair can quickly regain its full, safe height adjustment instead of being replaced by a new chair too soon.