Raised vent system won't stay in down position

Question

when pushing the up/down button, the vent will go up with no problem. However, when pushing the button to make it go down, the vent will go down but then go right back up. It won't stay down. The only way to keep it down is to turn off the breaker when it gets to its lowest point. Once there, the breaker can be turned back on and the vent will stay down.