Rain Sensor Troubleshooting and Repair

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A rain sensor hooked up to an irrigation or sprinkler system can help you save money and water. The sensor is connected to the wiring of an automatic sprinkler or irrigation system so that power must flow through the sensor in order to open up the valves for water to get out. The sensor detects rain and breaks the circuit, preventing those valves from opening up.

Knowing these basic principles of how the rain sensor works is the key to troubleshooting your malfunctioning system. Below are steps to take to solve the 2 most common rain sensor problems. The first 3 steps are for sensors that never let the sprinklers turn on, the latter 3 are for rain sensors that never shut them off.

Materials Needed

  • Wire Strippers
  • Wiring
  • Alligator Clips
  • Electrical Tape
  • User's Manual

Step 1 - Inspect Hygroscopic Disks

Examine your sensor to ensure nothing is obviously wrong with it. Above all, check that the hygroscopic disks are dry. The hygroscopic disks are what absorb water during a rainfall, which causes them to inflate and depress a switch that turns off your system. If they are dry, be sure that no debris of any kind has made its way in there to press the switch.

Step 2 - Inspect Wiring

Give all of your wiring a good inspection. This is especially important for systems with wires that lead from your switch (containing the hygroscopic disks) to the controller for your sprinkler system. Be sure that there are no breaks in the wiring to or from the switch, and that everything is connected in the proper places.

Step 3 - Test Power

Use wire strippers to carefully uncover a small portion of the copper wires leading to and from the switch. Connect a "jumper wire" between the exposed sections using alligator clips, then go turn your sprinkler system on. If the system begins to water, it means your wiring is fine, but the switch is bad and needs repair or replacing. You may need to replace the switch or call someone to repair it. Refer to your user's manual for more detailed troubleshooting instructions.

Step 4 - Location And Wiring

If your rain sensor fails to turn your sprinklers off, look for any obstructions that might keep rain from hitting your rain sensor. If necessary, purchase a wireless sensor so you can put it anywhere. Also, evaluate your wiring to be sure everything is connected properly (though wiring problems usually keep the system from turning on at all).

Step 5 - Check Bypass Switch

Many modern rain sensors come with bypass switches that allow power to reach your water valves regardless of wetness. If this is the case with yours, check that the bypass switch is turned off and working properly.

Step 6 - Inspect Hygroscopic Disks

Be sure that your hygroscopic disks are dry. If they are wet, orthey are simply taking far too long to dry, move your switch to where it always gets hit by direct sunlight after a rainfall. Also, if your rain sensor allows it, adjust the sensitivity of the switch so that it takes more water absorption for the disks to hit the switch. 

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