Stupid question, have you tried priming the pump again, just in case?
Have you taken apart the nozzle to make sure it's not clogged?
Have you tried taking out the zipdrip to see if if works then?
Unless your pump is more than a a couple feet away from the reservoir, it shouldn't matter whether it's above or below.
You might try the ideas above to see if they work. If you know water is getting to the zipdrip, my first test would be to remove it and run the system.