If your well pump suddenly stops working, don’t panic just yet. Before digging up the pump or calling a pro, take a good look at the control box. It’s often the first thing to go—and luckily, it’s one of the easiest things to check and replace.
This guide will walk you through how a control box works, what commonly fails, and step-by-step instructions to help you diagnose the issue. Let’s start with the basics.
What Is a Well Pump Control Box?
A control box manages the start-up and run cycles of a submersible well pump—especially 3-wire pumps. It typically contains:
- Start capacitor – Boosts torque to start the pump motor
- Relay – Helps engage the start capacitor when needed
- Overload protector – Prevents overheating or short-circuit damage
If any of these parts fail, your pump may not run—or it might hum, click, or shut off unexpectedly.
Signs the Control Box Might Be the Problem
- Pump hums but doesn’t start
- No sound or response from the pump at all
- Breaker keeps tripping
- Burnt smell from the box or components
- Pump only starts after you tap or jiggle the box
Some of these symptoms can also point to a bad pump or pressure switch—but the control box is a cheaper, easier place to start troubleshooting.
Before You Begin: Safety First
Turn off power at the breaker before opening the box. Double-check with a multimeter or non-contact tester that no live voltage is present. You don’t want to mess with 240 volts blindly.
Step-by-Step Troubleshooting
1. Check the Power Supply
- Verify the breaker hasn’t tripped.
- Use a multimeter to confirm 240V is reaching the control box.
- No voltage? Trace back to pressure switch or main panel for issues.
2. Inspect the Box Visually
- Look for melted wires, burnt smells, or bulging capacitors.
- Wiggle connections gently to check for looseness or corrosion.
- If anything looks crispy or damaged, replace the box or affected parts.
3. Test the Start Capacitor
You’ll need a multimeter with microfarad (μF) testing mode. The capacitor will usually have a rating printed on it (e.g., 88–108 μF).
How to test:
- Discharge the capacitor (short terminals with a resistor or insulated screwdriver).
- Remove it from the circuit.
- Set meter to capacitance mode and measure across the terminals.
- If it reads significantly below the labeled range—or zero—it’s bad.
4. Check the Relay
The relay is responsible for switching the start capacitor in and out of the circuit.
Bad relays may click but fail to close, or they may stay permanently stuck—causing the capacitor to overheat or never engage.
How to test:
- Use continuity mode on your multimeter.
- Test across the coil (should show some resistance).
- Check contact terminals while pressing the relay—should go from open to closed.
- Any open readings or erratic movement? Replace the relay.
5. Measure Resistance to the Pump
If your control box checks out but the pump still won’t run, measure resistance to the motor windings.
- Turn off power.
- Disconnect wires labeled “R,” “Y,” and “B.”
- Use ohms mode to test resistance between pairs (R–Y, Y–B, R–B).
Readings should be consistent and in the expected range—typically between 2 to 15 ohms depending on motor size. Infinite or zero readings usually indicate a broken or shorted winding.
When to Replace the Control Box
If the capacitor is swollen, the relay is stuck, or the box smells burnt, replace the whole unit. Control boxes aren’t that expensive—often $40 to $100 depending on brand and horsepower. And replacing the whole thing is faster and safer than fiddling with single components.
Make sure to match the new box to your pump’s horsepower (½ HP, ¾ HP, 1 HP, etc.) and voltage (usually 230V).
Final Thoughts
A dead well pump doesn’t always mean you need to pull it out of the ground. Often, the issue lies right at the surface—in the control box. By checking power, capacitors, and relays step by step, you can zero in on the problem and save yourself time, money, and stress.
Not sure? Replace the box anyway—it’s cheaper than guessing wrong and calling in a backhoe.