There really isn't much to this system. You're probably looking at a clog or a pinched line, and the procedure for both is pretty much the same - pick up some extra line and run a temp straight to the nozzle. If it works then, work your way back along the line, plugging it in and testing it from every join, until you find the offending section, then replace that.
If it doesn't work with the temp line, check the nozzle itself.