If a solenoid is faulty, what is the first thing you should check?

When troubleshooting a faulty solenoid, checking the voltage at the solenoid is the most critical first step. This is because solenoids operate electrically, relying on a specific voltage to function correctly. If the voltage is absent or below the required level, the solenoid will not open or close, rendering it ineffective regardless of its physical condition or the controller's power status.

By measuring the voltage directly at the solenoid, you can quickly determine if the issue is related to the electrical supply or the solenoid itself. If the voltage is within the expected range, this suggests that the solenoid may be malfunctioning and may need replacement. Conversely, if there is no voltage, the problem may lie earlier in the system, such as with the controller or wiring.

Checking the physical condition of the valve, the controller's power, or the water flow rate can be important steps in your overall diagnosis, but they are secondary to ensuring that the solenoid itself is receiving the necessary electrical input to operate correctly.