I too had the same problem in that my Sears Carftsman 1/2 HP garage door opener started to give me problems as soon as fall, and the cold weather, began. I found that turning the Force Adjustment dial (the dial closest to the garage door, the other being the Contact Reverse dial)solved the problem. I just turned it slightly clockwise and I've had no problems since. Just make sure you test the door by placing a 2X4 under it and making sure it reverses upon contact. If it doesn't, you probably added too much force. Good luck.