My sister's Garage door won't stay closed. It's an automatic. As it travels to near the bottom, it stops and returns to the upward position.It is not obstructed, the channels are clear and the wheels turn freely. I thought it might be a problem with the balance of the door, but it moves fairly easily from top to bottom, and furthermore, it is a single spring setup where the one big spring is centrally located on a shaft that turns both pulleys at the ends evenly. The cable tension seems right and even both sides. Also, it is only an eight foot wide door. Lastly, even with the door detached from the drive (Manual Mode), the carriage will not stay in the down position. I tried adjusting the down force and down position, but it didn't help. There is no infrared sensor. What could be the cause of this problem?
Springs is wound to tight.
The door in manual should be about to be stopped in any position and have it not move if it's set right.
Trying to adjust that spring without knowing what your doing can cause damage to life and limb.
You need to check the track thet the door operator rides on. If it is doing it with the door unhooked as you say then the guilty part has to be the part that rides on the track or the track itself. Get a ladder and watch it from above to see where it reverses and check that area.