Step by step guide how a VALVES solenoid works:

    When an electrical impulse is transmitted to the solenoid (black cylinder with wires), an electromagnetic field causes a small metal plunger in the solenoid to move upward.
    When the plunger moves upward, a small hole (port) in the valve is uncovered. Water in the chamber above the closing mechanism (either diaphragm or piston) flows through the port and out of the valve, relieving water pressure needed to hold the valve closed.
    At this point, the pressure of the incoming flow of water is now greater than the pressure in the chamber above the piston/diaphragm, and the force of the water pushing up underneath the piston/diaphragm opens the valve.
    When the solenoid is DE-energized, the plunger moves down, closing the small port. Water flowing through a small hole in the closing mechanism refills the chamber above the piston/ diaphragm and builds up pressure. The increased pressure forces the piston/diaphragm downward, thus closing the Valves.

Here are a few things to check in determining if your solenoid is bad

    The solenoid should make a distinct “click” and hum or vibrate when activated. Try unscrewing the solenoid and swapping it with a nearby valve of the same model. Using the “Manual Start” on your timer, check the station again to see if the borrowed solenoid activates the valve.
    Check for any visual hints that the solenoid has failed, such as rust? or that the wire connections are in waterproof connectors.
    You can also have your solenoid tested with a multimeter. An electrical resistance test should typically indicate a reading between 20 and 60 ohms for a solenoid that is operating properly.
    Check for a missing or broken solenoid O-ring.

How to adjust a valve solenoid?

    Turn the solenoid (the black device with two wires coming out of it) to the left 1/4 turn. This will allow the valve to manually turn on.
    To turn the valve off, turn the solenoid to the right until it is hand-tight

How to replace a solenoid?

1. Disconnect both wires connected to the solenoid.
2. Turn solenoid counter-clockwise until completely loose and free from Valves.
3. Screw in new solenoid by turning clockwise. Do not over tighten. Only handtight.
4. Connect both wires to new solenoid using waterproof caps.

How to clear a clogged solenoid.

Sometimes the plunger inside the solenoid can become stuck in the upward position due to dirt in the solenoid. Check for dirt impeding the movement of the plunger.To do this:

    Turn off the water and remove and disconnect wiring to the solenoid.
    Unscrew the solenoid by turning it counter-clockwise.
    Run water into the solenoid to dislodge dirt.
    Push a piece of wire into the small hole in the retainer at the bottom of the solenoid to see if the plunger inside will move up and down freely.
    If this does not resolve the issue, replace the solenoid.