Automatic sprinkler systems rely on clean pipes and steady water pressure to operate properly. If your sprinklers are showing signs of slowing down, erratic spraying or no spraying at all, chances are there is dirt trapped within the sprinkler lines. It's possible to flush your lines using no tools and removing the dirt. Once a sprinkler line is flushed out, the performance should return to normal.
Open the irrigation control box outside and identify the first zone on the sprinkler system. The first zone is typically the one closest to the supply pipe.
Turn the solenoid on top of the valve counterclockwise to begin the manual flow of water.
Inspect each sprinkler head on the zone for signs of dirt clogs. A clogged sprinkler will spray erratically or not at all.
Tighten the solenoid on the valve and watch as the sprinklers go down. Note the position of the last sprinkler to stop spraying. This is the last sprinkler on the zone.
Grab the top of the sprinkler that you have identified as the last on the line and turn the body counterclockwise until it releases from the plastic riser underground. This will expose the riser and give dirt that's trapped in your line a place to escape.
Turn the solenoid on the sprinkler valve counterclockwise again to start the flow of water. Water will gush out of the sprinkler riser that you removed. Allow the water to flush through the line for at least three minutes. After that time, tighten the solenoid to stop the flow of water.
Replace the sprinkler on the riser and tighten clockwise by hand. Any large particles of dirt that were trapped in the line should now have been flushed out.