mine is an older one, but if yours is anything like mine, you should be able to see the spray pattern when the unit is on. if its just leaking/ trickling and not spraying a good mist you can have one of a couple different problems. improper air flow which could be clogged filter, air leak in the metal line or the air pump isnt working correctly. another common problem is the nozzle could be burnt out or clogged.
quick and easy way of seeing if your air pump isnt working correctly, disconnect the metal line coming from the air pump and take a blow gun/ air compressor and apply light air pressure into the airline while the unit is plugged in. if it ignites due to a good mist than you know where your problem is. like i said, one of the vanes on my air pump was stuck and was not producing a good airflow which resulted in a bad mist/ no mist
here is what it should look like
http://i22.photobucket.com/albums/b331/kliped/IMG_20110926_135444-1.jpg