Heads Pop but no water!
Just turned up my system for the summer (I know- late as usual) and on one of my zones, all 4 heads pop up but only the first head in the line sprays. The other 3 are under pressure as they resist if pushed down and water will come out around the pop up if I move it around. IS this a cleaning issue or something else? All other heads in the system work fine but these 3 in a line don't want to work.