Garage door opener will raise the door but will not lower it?

On some types you have mechanical limit switches. Could be that the down switch is broken or not wired any more. If so they are inexpensive, about $10.00 or less.

Door closes but won't open... Stuck open-limit switch or loose wiring Inspect or replace open-limit switch and check wiring to open-limit switch.

Inadequate open force...Adjust per manual.

Door needs adjustment or maintenance, or door is binding due to expansion in hot, humid weather Check operation without opener.

Door opens but won't close Problem with safety-reverse system Test and adjust safety-reverse system according to owner's manual.

Stuck open-limit switch or loose wiring Inspect or replace open-limit switch and check wiring to open-limit switch.

Inadequate close force Adjust per manual.

At the bottom of the garage door, on each side, there are usually 2 sensors that look toward each other. If anything gets between these sensors, it will not shut for safety reasons. They have a small round lense on them, wipe them clean and make sure they are pointing direclty toward eachother (they may come out of alignment from something hitting one of them). Even a spider web or dirt can interrupt the signal.

If this doesn't work, check the switches directly on the garage door opener unit. They usually have 2 or even 3 little adjusting knobs. 1 adjusts how high the door should rise. 1 adjusts how low the door should go. and sometimes there is a third, that adjust the resistance it takes to make the door go back up automatically (like if the door hits something on the way down).

Just out of curiosity, you didn't mention if this happens with a remote control opener AND/OR the regular garage door opener. It could be the opener itself malfunctioning.

Are your electric eyes lined up at the base of the doorway? Is it a chain drive or screw type? how old is it. the point I'm trying to make is, a lot of your questions could be answered more accurately, if given more info.

Does your opener have a detector that looks for any obstructions in the way of the door? If so, that may be malfunctioning.

Check the safety beam system at bottom of doorway, the beams must be aligned with each other. --IC

Does the door do anything else unusual?