If the main lights on the garage door opener start flashing while the door is trying to close that is a warning to you that there is an issue that is preventing the door from closing. The flashing lights will start either after the door has started to close but then reversed or may start from the full open position before ever starting to close.
If they start flashing from the full open position in many cases that means there is an issue with the photo-cells either being blocked, out of alignment, of malfunctioning for some reason. If this is the case you should review our photo-cell sensor page for more information on troubleshooting that type of issue.
If the door does start to close but then reverses before the main lights start flashing there a few different reasons that the reversing may have occurred. It could possibly be an issue with the opener or the garage door itself.
If you have a Liftmaster, Chamberlain, or Craftsman garage door opener that will only travel a few inches in either direction that may indicate that the RPM sensor is bad or that the RPM sensor motor shaft has come unseated. However if the RPM sensor is the cause the the opener carriage will only travel exactly 4 inches in either direction. In addition the LED light on the motor head should be flashing five times.
If the opener is closing at least partly down into the opening before reversing then the place to start to look is around and behind the garage door tracks on both sides of the opening. It's very common for a broom or tool handle that is stored in the corner by the door falls over and goes behind the door track. Once the door hits that handle then it should stop and reverse and the lights will start. Obviously the solution is to move the obstruction and possibly secure it so it can't fall over again.
If the reason isn't clearly obvious like in the above two scenarios then you'll need to determine if it's a garage door or door opener issue. The next step is to pull the garage door opener red release cord to see if the door works smoothly and freely form full open to fully close when using it manually and that the garage door opener will run fully opened and closed while the garage door is disconnected and the opener isn't under load,
While working the door manually you should be making sure that the door is properly balanced by seeing if it will basically stay in the same position whenever you let go of the door, that it doesn't fly open on it's own or drop like a rock, and that it doesn't take much effort to lift the door all of the floor and/or to pull the garage door down into the opening from the full open position. If the door is out of balance then you should contact a professional garage door repair company to make the necessary adjustments or even change the torsion springs.
If the garage door works fine manually then the issue may be in the garage door opener and if the garage door opener won't run fully open or closed when the door is disconnected it's very highly likely the issue is in the opener. If it’s in the opener the issue may be in the worm screw, the belt, or the chain depending on the type you have or something under the motor cover like a gear or the RPM sensor or the main logic board. Look for the obvious but again it may just be easier to have a garage door opener specialist come out to the home to determine the cause and will most likely have any parts that are needed on their truck.
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