Another common cause for a loose chain could be the front sprocket breaking.
How to fix chain slipped of garage door opener.
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Check the breaker controlling the door opener and.
Ensure that the unit is plugged in the door isn t locked and if you are using a remote that the remote has batteries.
Make basic checks first.
Sprocket is at the end of the opener rail closest to the garage door opening.
Make sure the cable is inside the cable pulley and run the chain around the sprocket.
Tighten the chain and then turn the power back on.
Press the wall control button or remote so that the opener completes its close.
Place a stepladder near the motor and unplug the power cord for the motor from the electrical.
The chain is attached to a threaded rod that is attached to the trolley.
Open up the control box for your opener and you should see the chain control with two bolts one either side of the box.
If your garage door is closing fully and then reversing to open again then it may be due to a problem with the close limit switch.
Around this sprocket as well as the gear and sprocket at the motor.
When problems do occur you should know how to fix them easily and quickly.
One bolt will tighten up the chain the other loosen it.
Disengage the garage door from the opener by pulling down on the emergency pull cord to release the door trolley from the opener carriage.
Pull down the trolley cord to release the trolley from the chain arm and lower the door by hand.
How to put a chain back on an automatic garage door opener.
A new front sprocket costs.
Loosen the inside nut and back it off 6 8 turns back the outside nut off 5 6 turns this will give you some slack in the chain.