Garage door won't close without multiple tries
7yr old Chamberlain Liftmaster door won't close without multiple tries. Both sensor lights seem align fine, with steady lights on. LED on the motor does not lit, flashes couple of time upon re-press the button on remote. Manual lift/close the door is sooth, too.
Any idea what the problem is? I do observe that the lamp on the motor flicks if the door is opening or closing. Thx.