If the control unit is in “CLOSE” mode, then it will try and lower the door. The motor stops running when the cord goes slack. If the cord never goes slack (e.g. because the cord is not long enough or is pulled tight when in closed position), the motor will spin till the cord unwinds fully inside the motor control unit and then winds the cord the other way around the motor pulley (like a yo-yo) and then it will lift the door.
As the unit then thinks it’s closing the door, the upper limit switch has no effect, and the door jams open. If left unattended in this condition, the batteries will become prematurely exhausted.
We have created a video to detail the condition and how to avoid and resolve it at this link.
If this has happened because the cord is not long enough then either extend the cord or replace it. See this link if replacing the cord.
Otherwise, to correct the condition perform the following:
1) Turn off the power pushing the toggle switch up
2) Gently but firmly push the door down until the upper limit switch is released (it will be stiff due to the motor gearing)
3) Advance the Control Unit mode to “OPEN” using the MANUAL button
4) Turn on the power, pushing the toggle switch down. The door should lower and when the door has fully lowered, maintain tension on the cord by keeping it taught with your fingers (pulling away from the motor unit). At the end of its travel the unit will start to wind the cord back in and as it takes the weight of the door release the tension on the cord allowing the motor to lift the door again till it reaches the upper stop switch.
If this is not the problem and the door still will not close, then please also check that the cord is correctly routed as shown at this link.