Door sliding back down once the door is up all the way it s resting on the horizontal parts of the track and the resistance of the motor to turning because it is low geared should prevent it coming back down.
Garage door opener why the door slide back down.
Garage door opener problem.
Thank you for your question as to why the garage door will open all the way but slides back 6 inches.
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.
We recommend unplugging the garage door opener and then replugging it back in after any repairs or adjustments to reset the system.
It will be obvious if it is going bad.
If you garage door is lowering then reversing back to the open position there could be something obstructing the sensors.
You will have to take the cover off the motor unit to check the gear.
You need to check the door springs and the drive gear in the opener.