The motor runs. You hear it. The door stays on the floor. This is one of the more misleading failures a garage door produces, because a running motor sounds like a working system. It is not. The motor and the door are two separate mechanical chains, and the failure is almost always in the connection between them, not in the motor itself.
For a thorough breakdown of causes and what each symptom points to, read the full diagnostic guide on Garage Door Science. What follows is a structured checklist for working through the most common causes in order.
Before you touch anything
Unplug the opener from its ceiling outlet, or switch off its circuit breaker. Chamberlain’s service documentation is explicit: disconnect all electric and battery power before any service or inspection work on the unit. This is not a precaution you weigh against convenience. A motor that energizes while your hands are near the drive train will not warn you first.
Check 1: the door is no longer attached to the trolley
On chain and belt drive models, watch the trolley as the opener runs. If the trolley travels the full length of the rail and the door does not move, the door has been disconnected from the opener, almost certainly by the emergency release cord. This is the most common cause of this symptom.
Chamberlain’s support documentation covers reattachment: with the door fully closed, use the emergency release handle to reconnect the trolley, then test the opener. Their documentation also carries a warning that applies here. Weak or broken springs can cause a door to drop quickly with no warning. If the door feels heavier than normal when you push it by hand, or if it falls rather than lowers when you release it, stop. That is a spring problem, not a trolley problem. The next step is a technician, not a handle pull.
Check 2: the door lock is engaged
Residential sectional doors have a slide lock on the inside, usually a horizontal bar across the bottom panel. If that lock is engaged, the opener motor runs against a door that cannot move. The fix is to disengage the lock. This is worth checking before anything else because it takes ten seconds and costs nothing. The symptom is a brief hum followed by the motor stopping, often with a clicking or grinding noise from the drive assembly as the motor load exceeds what it expects.
If you are not sure whether your door has an active lock or a decorative handle, look at the bottom panel on the inside. A slide lock will have a bar that moves left to right. If it is in the center or toward the door frame, it is engaged.
Check 3: the trolley is caught on a stop bolt
At each end of the rail, a stop bolt or stop tab limits how far the trolley travels. If the trolley has ridden up against one of these and jammed, the motor runs but cannot drive the trolley in either direction. Chamberlain has a separate procedure for freeing a trolley from a stop bolt. Do not force the opener through multiple cycles while the trolley is jammed. Repeated stall loads accelerate gear wear inside the unit.
Check 4: the drive gear is stripped
Inside the opener housing, a helical gear meshes with a worm gear to transfer motor rotation to the drive chain, belt, or screw. When that gear strips, the motor runs freely with no load, and the drive assembly does not move. This is a repair, not a check you can confirm visually without opening the unit. The diagnostic indicator is that the motor sounds normal, no strain, no laboring, the chain or belt is stationary, and the door is confirmed to be properly connected.
LiftMaster lists replacement gear kits for chain drive models: the chain drive gear and sprocket kit (part 041C4220A, listed at $50.99) includes a helical gear, top hat assembly, worm gear, wear bushings, and grease. These are parts prices for specific listed models made after 1993. Labor to install is additional and varies. If your opener is more than ten or twelve years old and you are looking at a drive gear replacement, the decision between repair and replacement is worth working through before committing to parts. This breakdown of what to do when an opener quits covers the repair-versus-replace calculation with specifics.
When springs are the cause
Chamberlain’s documentation for this symptom lists broken springs as a possible cause of a brief hum followed by the motor stopping. A broken torsion spring means the door’s counterbalance is gone. The opener is trying to lift the full weight of the door with no mechanical assistance, which it cannot do. A standard residential opener is sized to assist a balanced door, not to lift an unbalanced one.
The signs: the door feels extremely heavy when you try to lift it by hand, or it drops sharply when you release it. If either of those is true, do not operate the door manually. Do not run the opener. A torsion spring under load holds significant stored energy. Replacing one requires specific tools and trained technique. This is a technician call without exception. For background on why this failure is dangerous and what the repair involves, the torsion shaft assembly explained article covers the physics and the procedure.
Diagnostic sequence
- Disconnect power to the opener.
- Check the door lock bar on the inside of the bottom panel. Disengage if locked.
- With the door fully closed, confirm the trolley is connected to the door arm.
- Check the trolley position on the rail. Confirm it is not jammed against a stop bolt.
- Push the door up by hand a few inches. If it feels extremely heavy or drops when released, stop and call a technician.
- If the door moves freely by hand and all the above checks are clear, reconnect power and run one cycle. If the motor runs and nothing moves, the likely cause is an internal gear failure. Call a technician with your opener’s model number ready.
The line between owner inspection and professional repair
The checks above are yours to run. The repairs are not, with one exception: disengaging a door lock and reattaching a disconnected trolley, with the door closed and power off, are within scope for an owner who can follow the manufacturer’s procedure step by step.
Drive gear replacement, spring replacement, cable work, and any adjustment to spring tension are not. These are not tasks where careful DIY closes the gap. They are tasks where the physics is indifferent to confidence. This guide to garage door repair draws that line in more detail for the full range of common repairs.
If the opener is running and the door is not moving and none of the owner-level checks explain it, give the technician your opener’s model number, on the label inside the housing cover, and describe what you heard: duration of the hum, whether the chain or belt moved, how the door felt when you pushed it by hand. Those details narrow the diagnosis before they arrive, and a faster diagnosis is a cheaper one.
Frequently Asked Questions
Why does my garage door opener run but the door doesn’t move?
The most common cause is that the door has been disconnected from the trolley, usually because someone pulled the emergency release cord. Other causes include an engaged door lock, a trolley jammed against a stop bolt, a stripped internal drive gear, or a broken torsion spring. Run through the checks in order before assuming the motor itself has failed, because motor failure is the least likely explanation when the motor clearly runs.
Can I reattach the emergency release myself when the opener runs but the door won’t move?
Yes, with conditions. The door must be fully closed before you reattach the trolley. With the door closed and the opener unplugged, use the emergency release handle as the manufacturer describes to reconnect the trolley to the door arm. If the door feels heavier than normal when you push it by hand, or if it drops quickly when you release it, stop. That points to a broken spring, and reattachment does not fix that problem.
How do I know if a stripped gear is why my opener runs but nothing moves?
A stripped drive gear produces a motor that sounds normal, with no laboring or straining, while the chain, belt, or screw sits completely still. The door must also be confirmed as properly connected to the trolley. You cannot confirm a stripped gear without opening the housing, so if the motor sounds normal, the drive assembly is stationary, and the door is connected, the working assumption is gear failure. A technician can confirm it and quote the repair.
What does a broken spring have to do with the opener running but the door not moving?
A torsion spring counterbalances the door’s weight. When it breaks, the opener tries to lift the full door weight unassisted, which exceeds what a residential opener is designed to do. The motor runs briefly and then stalls. The indicator is a door that feels extremely heavy when you push it by hand, or that drops sharply when you release it. Do not operate the door manually or run the opener again until a technician has replaced the spring.
How much does it cost to replace a drive gear in a garage door opener?
Parts cost depends on the brand and model. LiftMaster lists chain drive gear kits at roughly $28 to $51 for the parts alone, as of current manufacturer pricing, for specific models made after 1993. Labor is additional and varies by region and technician. If the opener is more than ten years old, compare the repair cost against a replacement opener before committing to parts, since an older unit may have other components near the end of their service life.
When should I stop troubleshooting and call a technician?
Stop troubleshooting and call a technician if the door feels unusually heavy when pushed by hand, drops quickly when released, or if you hear a loud bang that preceded the problem (a common sign of a spring breaking). Also call a technician if the chain, belt, or screw is stationary while the motor runs and the door is confirmed to be connected, since that requires opening the housing to diagnose. Spring and gear work are not owner repairs.
