Just because the door is open does not mean that the spring tension is fully released.
Proper chain tension on garage door opener.
If the tension is too loose the springs that help lift the door are ineffective.
By william machin you need proper tension on a garage door to operate the door by hand or with an automatic opener.
A properly adjusted chain will be above the base of the rail at its midpoint at inch for t rail or inch for square rail.
Using a screwdriver remove the cover on the garage door opener and then replace the spent battery with a new one.
Hold the garage door in this position by attaching a c clamp to the track at a point below the lowest door roller wheel.
If it does not open you need to replace the backup battery.
Use the wrench to loosen the lock nuts and turn the adjustment nut to set the slack in the chain.
Chain adjusts by shortening the chain itself.
There may be an adjustment linked to the chain or an adjustment to the length of the door opener track.
Both adjustment types should be done with the door closed and disconnected from the opener using the emergency release.
To achieve proper tension be sure to release the door from the opener before making any adjustments.
This is true even if you have a garage door opener.
Usually a pair of nuts are associated with the locking mechanism while one is concerned with the adjustment of the chain.
Replace the batteries in the door remotes.