The Acorn 180 is a reliable curved stairlift — but like any mechanical device, it can occasionally show a fault. One of the most common is the OSG (Over Speed Governor) fault, shown on the display as code F7. This guide explains what it means and what to do.
The Over Speed Governor (OSG) is a critical safety component in the Acorn 180 stairlift. Its job is to monitor the speed of the carriage. If the stairlift begins to move faster than its designated safe speed, the OSG activates the brake mechanism to bring it to a controlled stop — preventing accidents or injury.
When the OSG activates, it shows on the display as code F7.
An OSG activation is a safety-critical event. Do not continue to use the stairlift until the fault has been properly diagnosed and cleared by a qualified stairlift engineer.
An OSG fault typically indicates that the stairlift believes it is moving faster than its designated safe speed. When this fault occurs, the lift will stop operation to protect the user.
The fault can be triggered by a range of issues — some simple, some complex — so accurate diagnosis matters.
The speed sensors that monitor the stairlift's movement may have become damaged or unreliable.
Loose or damaged wiring can interrupt the signal between the OSG and the control unit.
Worn gears, motor components or rollers may cause the OSG to misread speed data.
Before calling us, there are two simple things you can check that may resolve the fault:
Look along the full length of the rail. Any object, loose fitting, or debris on the track can cause irregular movement and trigger the OSG. Clear anything obvious — but never put your hands near moving parts.
Switch off the stairlift at the mains or isolator. Wait 30 seconds. Switch it back on. This can clear minor faults caused by a temporary glitch.
If the OSG fault returns after clearing obstructions and resetting, call an engineer. Never open the carriage, remove covers, or attempt to reset the OSG mechanism yourself. Stairlifts are heavy mechanical devices — incorrect handling can cause injury or further damage.
Call us immediately if:
Our engineers carry the tools and diagnostic equipment to identify exactly why the OSG has triggered — whether it's a sensor, wiring, or mechanical issue.
Regular servicing is the best way to prevent OSG faults from occurring in the first place. An annual service by a qualified engineer includes:
Regular servicing keeps your Acorn 180 running safely and prevents faults like the OSG from occurring. Call us to book yours.
📞 0800 567 7033Quick answers to the questions we hear most about OSG faults.
The Over Speed Governor (OSG) is a safety component that detects if the stairlift is moving too quickly and activates the brake if so.
Code F7 indicates the safety gear has activated due to an OSG fault. The stairlift has stopped to protect the user.
You can clear obstructions and reset the stairlift — but if the fault returns, an engineer is needed. Don't open the carriage or attempt to reset the OSG mechanism yourself.
Common causes include faulty speed sensors, wiring issues, mechanical wear, or an obstruction on the rail.
No. Do not continue to use the stairlift until the fault has been diagnosed and cleared by a qualified engineer. Call 0800 567 7033.
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