A faulty solenoid is one of the most common causes of irrigation problems — a zone that won't turn on, a valve that won't shut off, or a controller that seems to be working fine but nothing happens in the yard. Catching a bad solenoid early saves water, prevents overwatering or dead zones, and avoids costly service calls.
What Is a Solenoid?
A solenoid is an electromechanical coil that sits on top of your irrigation valve. For most systems when your controller sends a 24V AC signal, the solenoid energizes, creating a magnetic field that lifts a plunger and allows water to flow through the valve. When the signal stops, the plunger drops and the valve closes. It's a simple but critical component in any automated irrigation system.
Signs of a Bad Solenoid
- A zone won't turn on even though the controller is sending a signal
- A zone won't turn off (valve stays open)
- You hear a buzzing or humming at the valve but no water flows
- No audible "click" when the zone activates
- Controller shows an error or short-circuit warning for that zone
Tools You'll Need
- Digital multimeter (with resistance/ohm and AC voltage settings)
- Flathead or Phillips screwdriver
- Spare solenoid (for a swap test)
- Wire strippers or connectors (optional)
Step-by-Step Testing
1. Manual Activation Test
Before reaching for a multimeter, try activating the valve manually. Most irrigation valves have a manual bleed screw or a twist-to-open collar. Turn it slightly counterclockwise — if water flows, the valve body is fine and the problem is electrical (solenoid or wiring). If no water flows manually, the issue may be with the valve diaphragm or water supply, not the solenoid.
2. Resistance (Ohm) Test
This is the most reliable test for a solenoid.
- Disconnect the solenoid wires from the controller or valve wiring.
- Set your multimeter to the resistance (Ω) setting.
- Touch the probes to the two solenoid wires.
- A healthy solenoid typically reads between 20–60 ohms. Most residential solenoids fall in the 25–50 Ω range.
- A reading of 0 Ω (or near zero) indicates a short circuit.
- A reading of OL or infinite resistance indicates an open circuit (broken coil).
Either extreme — short or open — means the solenoid needs to be replaced.
3. Voltage Test at the Valve
If the resistance test passes but the zone still won't activate, check whether the controller is actually delivering voltage to the valve.
- Set your multimeter to AC voltage (VAC).
- With the zone activated at the controller, touch the probes to the zone wire and the common wire at the valve.
- You should read approximately 24–28V AC.
- If you're getting voltage but the solenoid isn't clicking, the solenoid is faulty.
- If you're getting no voltage, the problem is upstream — check the controller, wiring, or zone terminal.
4. Swap Test
When in doubt, swap the suspect solenoid with a known-good one from another zone (or a new spare). If the zone starts working, the original solenoid was the problem. This is the fastest confirmation method when you have a spare on hand.
When to Replace the Solenoid
Replace the solenoid if:
- Resistance is outside the 20–60 Ω range
- Voltage is present but the valve won't open
- The solenoid body is cracked, corroded, or visibly damaged
- The swap test confirms the original solenoid is faulty
Solenoids are inexpensive and straightforward to replace — typically just unscrew the old one and thread on the new one. Make sure to match the thread size and voltage rating (most residential systems use 24V AC).
Get a Replacement Solenoid
Sprinklershop.ca carries a wide selection of replacement solenoids compatible with the most popular valve brands including Rain Bird, Hunter, Orbit, and Irritrol. Whether you need a standard 24V AC coil or a specialty latching solenoid for battery-operated systems, we have you covered.