It will be obvious if it is going bad.
Garage door opener why the door slide back down.
Thank you for your question as to why the garage door will open all the way but slides back 6 inches.
The one that is not is not strong enough to hold door up on its own but strong enough to still open the door.
Check to be sure these two sensors on either side of your garage door.
We recommend unplugging the garage door opener and then replugging it back in after any repairs or adjustments to reset the system.
Slipping down a few inches after opening posted by nashbamafan on 5 10 16 at 12 35 pm to sicboy probably have 2 springs above door and one of them is broken.
It can also be caused by dirt on the sensor eyes loose or corroded wire connections at the sensors or the motor head or just that the sensors have gone bad and need to be replaced.
You will have to take the cover off the motor unit to check the gear.
If you garage door is lowering then reversing back to the open position there could be something obstructing the sensors.