Testing and replacing valve solenoids/wiring

You can prove that the Irritrol Rain Dial RD600 series controller/timer is likely the problem and not the valves (or power/transformer) by bypassing the timer with this simple test.

Important: Make sure the water is turned on to the valves.  People sometimes spend hours troubleshooting the system, only to find out that the water had been turned off to it.  Typically, there are valves are in a ground box near where the water enters your house.  See this link for photos of a typical valvebox, valve and solenoid.

This page contains two sections;
If you just want to try replacing the solenoid, go to step 2.
If you want to do more testing to be sure the solenoid is the problem, start with step 1.

  1. Advanced solenoid testing procedures
  2. How to replace the solenoid.


(Or you could just try replacing it, it’s not hard and is usually the problem; see step 2 below)

a. If you have a multi-meter to test the irrigation valves:

The best way to check this is with a multi-meter.  Turn off the power to the system and set your meter to measure resistance (Ohms or the symbol Omega).   The first measurement is done at the timer where the valve wires connect to it. Usually, this is in a separate terminal/connector board behind or at the bottom of the timer.

If the solenoid is good, it typically measures between 20 to 60 ohms.    You typically measure between the valve wire and the common wire that is often labeled VC or VCOM or COM.

If it measures between 0 and 20 ohms, or an infinite or ‘open‘ condition, you probably have crossed or broken wires, or more likely a bad solenoid.

Take a second measurement at the valve box (usually in the ground) by measuring between the corresponding wire colors that you measured at the timer’s connection circuit board.  Usually, you disconnect the ‘wire nuts’ connected to both wires of the valves you’re wanting to test.   Note that the common wire is usually connected to one wire from each valve.   See the link to a wiring diagram here.

Its common for a valve solenoid to fail, but less common for a transformer to fail.   If the timer shows a display and indicates that it’s getting power when there is no backup battery connected then you can almost guarantee that the transformer is fine. Here’s a page on testing the transformer specifically.  It’s best to go this page first.

b. If you don’t have a  multimeter, you can do some checking this way:

If you’re getting a blown fuse or the FUS message, do not perform this step.  Look at this page instead.

Note, an inexpensive meter can be purchased for around $15-$20, it’d probably make more sense to just buy one since it makes this troubleshooting much easier and is more thorough and reduces the possible stress on the transformer if a valve is actually shorted. Get one with two probe wires and a dial that lets you select different settings like AC, DC, and voltage ranges down to 24V.

With this test, you basically connect one valve wire directly to the 24VAC screw terminals.

    1. Unplug the timer’s ribbon cable from the back of box.
    2. Disconnect (unscrew) one of the valve wires (e.g., connected to screw terminal #1 of the back of the connector board that sits behind the control module)
    3. This step will connect one of the valve wires directly to 24volts. Touch and hold it directly on (only) the right-most of the two 24VAC screw terminals (touch it for several seconds, long enough to notice if the valve 1 turns on or not, but not too long.  You don’t want the transformer to be damaged by trying to turn on a solenoid that’s shorted).
    4. If the Rain Dial Transformer and valve are good, the valve should turn on within a few seconds.
      1. If you’re reading this because you see the FUS message, you should not do the following step and just replace the solenoid. Otherwise, you run the risk of putting a shorted solenoid directly on the transformer without the fuse to protect it and the transformer could be damaged. If you’re not getting the FUS message, continue.
      2. If it doesn’t come on, try moving the wires from the VC screw terminal to the left most of the 24VAC terminals.  This will bypass the fuse and connect the other wire of the valve directly to 24volts.  Then repeat step C above.  When you touch the wire to the terminal, both wires will be connected directly to 24volts.
    5. If it comes on, you know that the valve and wiring to it are good.  You also know the power to the transformer and the transformer is good.   Thus, the timer and/or back connector board are likely the problem; send it in for repair.
    6. If it does not come on, you likely have a problem with the fuse, power to the transformer, or the transformer has failed.


2. Replacing the Solenoid:

  1. Take a picture of the full valve and solenoid to your local landscape supply store and buy a replacement (~$15). (E.g, SprinklerWorld, or other, but usually not HomeDepot or Lowes or you’ll have to buy the entire valve).
  2. Show them the picture and they’ll probably reach under the counter and sell you a replacement; it’s a very common request.
  3. Turn the water off,
  4. Disconnect the wires to the solenoid.
  5. Unscrew the solenoid (Counter clockwise) and replace it with the new one.
  6. It should be tightened just hand-tight, not too hard.  Also note that if it has an on/off indication, you want it to be ‘off’ so the sprinkler timer can over-ride it and turn it on.

A note about the fuse: See the Checking the Fuse page for more info.

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