Garage door opens only part way then closes. Its a caftsman door opener from sears 1/2 hp, dont know how old it isw.

the remote can use only 1 button to open and close if programmed right
open the lid of the seers control box and press the program button then use a different button on the remote to open and close
It would appear that the seers unit is also made by chamberlain

Check the door springs and also remove the cover from the motor unit and check the drive gear. The door spring could be broken or the drive gear may be stripped.

The sensors only work when the door is closing.

Door sensors are not working. Check if lights are on both sides.
Might be misaligned or one is bad.
Door will close if you hold in the garge close button until it's all the way down.
And it will open on it's own.
You can get these off ebay.

Loosen the chain enough so that you can remove it from the sprocket above the motor unit. With the door closed run the motor until the sprocket turns clockwise and stops. With everything attached replace and tighten the chain. Some adjusting of the up and down limits will probably be required.

Check your door sensors. They have probably been bumped. Tweak them until they are pointed at one another and the small light on each one is lit and not blinking.

Try this link
http://www.garagedooropeners.us/helpgifs/chamberlain_troubleshooting.html

You should check the gears inside the box, After years , the gears get dry and die, you can by online or from Sears the kit and replace the old gears. I just changed mine...not too difficult :) .

You say it only opens two feet?? Then closes?? If I may if you a little bit more costly option. Dont replace the gears. They used to be really good 8 years ago but the way they make the gears now there too soft and often strip out much faster. I would suggest that you do what we call a motor head change out. Take off your old chain drive motor head and buy a new one. Pretty simple. Two things though one always make sure you put the new one in with the door down. And the traveler in the down position ( The traveler is the metal thing hooked up to the chain) but far and your gear that you have it sounds to me that you dont have the gears close enough.. but 100 percent on that but a door should never close on it own. It's not safe.

You have a stripped gear inside the opener

NOT SURE WHAT UNIT YOU HAVE .
ALL OPENERS HAVE AN ADJUSTMENT TO TELL IT HOW FAR TO GO UP AND HOW FAR TO GO DOWN. LOOK ON THE SIDE OR UNDER A LIGHT COVER.IT HAS TO BE THERE SOMEWHERE