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Zone 2 of my irrigation system has 6 pop-up sprinkler heads but the last two do not pop up, nor is there any water coming from them at all. They are completely dry, even in the flex lines they are attached to. My assumption is that there is a break in the main PVC line after the last working head. So, I have been digging up this particular line to find the break, but with no luck. It's about 30 feet long and I'm about halfway with digging this line up. I was certain the roots from a nearby Queen Palm would have been the culprit but after clearing that area with no breaks I'm wondering if something else could be the problem, especially since I am seeing no water coming out of the ground after letting the zone run for a while. So, could this be a problem with the valve or is it definitely a break that I've yet to find? Should I keep on digging until I find it? This irrigation system was not being used for at least 3 years and only recently has been turned on for the first time, so I was expecting some work to be done.

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If you have a leak, you will find it in the last spot you dig. Seriously though... one thing I might try is turn off the other sprinklers in the zone except for the two that don't work and see if they now work with the others off. That could indicate loss of pressure/flow in the system that might not always mean a leak. Water Co might have changed something. or could mean leak is anywhere on that zone. If still no water then keep digging past the last working one. Likely a break. If pipe is deep may not see the leak above ground. –  OrganicLawnDIY May 12 at 4:42
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If you can remove the sprinkler heads completely (mine can screw off), you can test if there is water flow. My line got some sand particles on install day, and ended up clogging the sprinklers at the end of the line. –  Hightower May 12 at 12:49
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Clogged in head filters and so much sand washed in that the sliders have seized since it's the end units. As @Hightower recommends, undo the threaded collar, pull the head out and see if you have water flow. If not then there's a solid blockage as usually if the line's broke enough to kill two end sprinklers, you'll have a soil quicksand mushy spot at the break and all the upstream sprinklers will be barely functioning. –  Fiasco Labs May 12 at 14:52
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To answer my own question after solving the issue...

If the problem is only at the last two heads and the first ones are fine, then it is definitely a problem occurring after the first heads and unlikely to be valve-related (though not impossible). A broken line is most likely in this case, since your last two heads are dry in the risers and flex lines (it's not the heads merely being clogged). Broken pipes can usually be revealed by looking for muddy soil after running the zone for several minutes, especially if it's a break so bad it is completely stopping your last two heads from receiving any water pressure at all. If the soil has become impacted inside the broken pipe it may be difficult for the water to escape and reveal the break.

One common method to this problem is to increase the water pressure to the break and force the water out. It will not be so much pressure that damage can be done to the PVC joints and heads (as it will only be for a few minutes nor will the PSI be any higher than the output of your main water line or jet pump). This increase in pressure can be done by capping off all the sprinkler heads in the problematic zone. This will put more force on the possible break and on the soil that may be clogged in the pipe. After several minutes the leak may reveal itself. I'm sure there are several ways to cap off sprinkler heads, but the most common and simplest method is to buy PVC threaded caps (3/4" or 1/2" depending on your risers) that screw right on to the risers.

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In most cases you don't need to buy caps. With spray nozzles and I believe gear rotors you can turn the screw on the top all the way clockwise to shut off the flow. Impact sprinklers I don't think can be shut off this way. Your answer is written in the third person. What did you actually do to solve the problem and where did you find the leak? –  OrganicLawnDIY May 26 at 4:44
    
Great tip about turning down the nozzles to shut off the heads. I didn't realize turning the nozzles down all the way would be equal to capping off the heads (I thought they might still seep water). I found the leak by capping off all the heads on the zone (except the two that weren't getting any water anyways) and the increase in water pressure revealed the leak which was located at the elbow under a riser on a head near the drive way. It was probably run over at some point in the past. This head was actually completely buried and I had no idea it was there. –  PJS1987 May 26 at 23:48
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I should have left an answer and not a comment as my first response. Had to skip over some details to fit. For the driveway head if you ever want to replace the riser with Swing Joint/Funny pipe type deal it will minimize the chances of that happening again. Sprinklers near driveways tend to get driven on and walked on a lot. The flexible pipe in the swing joint won't crack like a riser will. –  OrganicLawnDIY May 27 at 0:42
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