From time to time, we get a call at A‑dec Customer Service that goes something like this:
"Help! I came into work this morning and my dental chair won’t move."
"My delivery system touchpad says, 'The chair stop plate was activated,' and my chair seems to be disabled."
"I can raise my dental chair up higher, but I can’t lower it down."
If you’re encountering this problem, don’t worry! There are a few quick fixes you can try on your own. And when in doubt, you can always call A‑dec Customer Service—we’re happy to help.
(A quick note: while this article provides helpful advice, always consult your chair's instruction for use or service guide for detailed information. These instructions apply to A‑dec 511, 411, and 311 dental chairs.)
What is a chair stop switch on an A‑dec dental chair?
A‑dec 511, 411, and 311 dental chairs include a chair stop switch, also known as a limit switch. This is a safety feature designed to stop a dental chair from moving down after it encounters an obstacle, helping prevent injury or damage to equipment. The main stop switch is located behind the stop plate in the hydraulic base of the chair.
How is a chair limit switch activated?
Any time the stop plate is pressed, it will halt the chair. A warning is displayed on the delivery system touchpad: "The chair stop plate was activated. Check for interference." While the stop switch is activated, the chair can be raised up, but it can't be lowered down.
The stop switch is usually activated by pressing down on an obstacle (for example, foot controls may have become wedged under the chair), or when a doctor or hygienist inadvertently kicks the stop plate.
It is also common for the stop switch to be accidentally pressed during operatory cleaning, especially if the chair is raised up to its maximum height. Occasionally, this can result in the stop plate becoming stuck in a pressed-down position.
How to fix a dental chair disabled by a chair stop plate
You can always call A‑dec Customer Service for help troubleshooting your dental chair, but we recommend trying these steps first to see if it's an easy fix.
- Check that the power is on for your dental chair and delivery system. (The chair power button can sometimes get pressed accidentally during cleaning.)
- Gently shake the chair stop plate to make sure it isn't stuck in a depressed position. Wait 10 seconds after shaking the stop plate free, then try lowering the dental chair again.
- If you have an A‑dec 411 or 311 dental chair, remove the seat (see instructions in the service guide) and clean the backrest slide tracks with warm soapy water. On rare occasion, these tracks can become gummed up with debris or sticky substances that increase the friction of the backrest as it declines and inclines. If the friction becomes too high, it may be enough to cause the stop switch to activate.
If those solutions don’t work, call A‑dec Customer Service. We're happy to help you troubleshoot your problem! And if your stop switch sensor needs replacement, we can help you get started.
