When you see you garage door opener lights flashing and the garage door will not close it could be the lock button or the safety reversing sensors.
Garage door will not close light on.
There are a few things which can cause this.
Start by checking if.
The table below shows how to identify the issue with the diagnostic.
Garage doors sometimes seem to have a mind of their own often deciding when and how far they want to open or close.
When the garage door does not close and the lights flashes it means the problem is with the safety sensor.
Sometimes the fix can be as simple as replacing the batteries in the opener.
This is of course a safety feature to prevent the heavy garage door crushing anyone or anything that might be in the pathway of the door when it comes down.
For the door to close correctly without reversing the safety sensors need to be aligned perfectly and there should be nothing in the way of the light beam.
With the diagnostic feature on craftsman you can know what exactly the issue is.
To prevent the garage door from injuring someone in the door or damaging an item in the way of the door all models of liftmaster garage door openers come installed with a safety sensor.
If anything interrupts this beam of light the garage door will not close and the ceiling light on the opener mechanism will flash as mentioned in the previous step.