In an automated irrigation system, the controller opens and closes one valve at a time by sending power to the valve through a pair of wires. The valve sends water from the main trunk line to a group of sprinklers. The valve and its group of sprinklers are called a zone. The point of connection is where the main trunk water line connects to your home's water supply and should include a main shut-off valve and backflow prevention. When the water won't come on, you need to evaluate things systematically to find the cause.
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Nothing Happens At All
If none of your sprinkler zones come on, start with a quick check on the two most likely problems. Verify that the main shut-off valve at the point of connection is turned on and that the controller has power. Many newer homes have ground fault circuit interrupter receptacles in garages and outbuildings. Just seeing a plug properly plugged into a receptacle does not confirm that it has power. Likewise, many controllers have battery backups that will display current clock information, but will not operate a zone. If there is unquestionably power to the controller and the main shut-off valve is open, and the controller is properly programmed, yet nothing will come on, go to a valve box and manually open a valve. If the valve will open manually and send water to the zone, your controller is faulty or all of the wires from the controller have been cut.
Confirming Controller Operation
Open the controller to the connection points. Start a zone. Hold one probe of a voltmeter against the connection point for the zone that should be running and the other probe on the common connection. The voltmeter should indicate 24 volts (any measurement between 24 and 30 volts-AC is acceptable). If it does not, check the wires coming into the controller from the transformer. If they show 24 volts, but the output connections do not, the controller is faulty. If the wires from the transformer do not show 24 volts, either the transformer or the circuit supplying the transformer is faulty.
Confirming Wiring Integrity
If the controller checks out OK, but the zones will not run, the wire from the controller to the zones may have been cut. Open a valve box and disconnect the solenoid from the pair of wires that run from the valve to the controller. Connect the wires running to the controller to a voltmeter. Switch that zone on from the controller and observe the voltmeter. If it does not indicate 24 volts, the wire is damaged somewhere between the valve and the controller. Rent a line tracer and trace the line until you find the break, dig up the break and splice the line.
Problems With One Zone
Open the valve box and manually open the valve. If the zone will operate manually, the problem is electrical in nature. The most likely problem is a faulty valve solenoid. Take the solenoid off the valve and disconnect the wires. Confirm that the wires are supplying power to the solenoid by using a voltmeter as described earlier. With 24 volts supplied, connect the solenoid. You should be able to see, hear and feel the solenoid activating. If not, replace it.
All Sprinklers in a Zone Seep
If all the sprinklers in a zone seep all the time, the valve is not closing completely. Either foreign matter is preventing the valve seat from sealing or the diaphragm is torn. Open up the valve, clean and inspect everything and replace parts as needed.
One Sprinkler in a Zone Seeps
If one sprinkler in a zone seeps water after the zone valve closes, it is most likely the lowest point in the zone. Many sprinkler models have check valves that can be installed on the sprinkler that is the low point in a zone. If yours does not, there are check valves that can be installed in the line immediately before the sprinkler connection.
Problems With Sprinklers
If a sprinkler doesn't rotate, it has to be replaced. There are no serviceable parts in a modern sealed rotor body. If a sprinkler won't pop up all the way or won't go down all the way, take the rotor body out of the housing and look for foreign objects trapped between the rotor body and the spring. Clean, reassemble and test.