Office Chair Problem

I bought this office chair from OfficeMax I think a couple years ago. The chair has an adjustable height. Lately when I sit in it, if it's in the maximum height, which I prefer, it slowly starts to lower itself while I'm sitting in. After 10-15 minutes, I'm back at the bottom again, so I have to readjust the height again. I like the chair, but this is annoying. Anyone know what's going here or possibly suggest a remedy. I tried looking on the chair, but there's no model number on it. OfficeMax doesn't keep purchase history more than 150 days. I can't find who made the chair to ask. Thanks for any help.

It may be hydraulic and the air escape valve is not closing properly.
If you're good with your hands and rip it apart, you may be able to fix it.

Busted Hydraulic cylinder. It's pretty common on cheaper chairs after using them. If you can find a matching cylinder then you can replace it. If not you have to replace the entire chair or live with the sinking.

I once had a chair that did that. It wasn't the lift, but the lever controlling it.

Shimmed something somewhere on it, and all was well.

Chair is dead. Time to replace it. Lifts can't typically be repaired and they cost more than buying a new chair.

Quote from batterycharger : I once had a chair that did that. It wasn't the lift, but the lever controlling it. Shimmed something somewhere on it, and all was well.

I know what you mean. Like a fork type piece of metal that iss activated by the handle.

Yes, I can't describe it. That chairs still in use in the attic, and holds up (no pun) fine. Without the shim it's useless.