Answer: Pop up sprinklers rely on water pressure to pop up. If the water pressure is okay, then the heads might be clogged. Over time, dirt, sand, algae, hard water deposits and other debris can cause a sprinkler head to become clogged. Most heads have removable nozzles and filters than can be removed and flushed out with clear water. Try removing one of the offending sprinklers and dismantling it to clean it. If after cleaning it still doesn't pop up, you may want to simply replace it. They're relatively inexpensive.
Best wishes with your sprinkler system.
Q&A Library Searching Tips