Well Pump Control Box: What It Does & Troubleshooting
Quick Answer: Control box provides starting power for 3-wire submersible pumps. Contains capacitor and relay. Only 3-wire systems have one (2-wire motors have built-in controls). When pump won't start, check control box first—replaceable without pulling pump. Cost: $50-$200.
What Is a Control Box
Purpose
- Provides extra starting power
- Motor needs boost to start under load
- Capacitor stores/releases energy
- Relay switches capacitor in/out
Components Inside
- Start capacitor: Stores energy for starting
- Run capacitor: Some have this too
- Relay/contactor: Switches circuits
- Overload: Protects motor (some boxes)
Location
- Mounted on wall near pressure tank
- Gray metal box
- Wires run from box to well
- Easy access for service
Why Above Ground?
- Serviceable without pulling pump
- Capacitors easier to replace
- Components stay dry
- Diagnosable with multimeter
2-Wire vs 3-Wire Systems
3-Wire Systems
- Has control box
- Pump has 3 wires to surface (plus ground)
- Common for 3/4 HP and larger
- Capacitor and relay above ground
- Easier to troubleshoot
Advantages
- Control box replaceable without pulling
- Most failures are above ground
- Lower labor cost for repairs
2-Wire Systems
- No control box
- Pump has 2 wires to surface (plus ground)
- Controls built into motor
- Common for smaller pumps (under 1 HP)
Disadvantages
- Any control failure = pull pump
- Higher repair cost
- Can't test controls easily
How to Tell Which You Have
- Look for control box on wall
- Count wires going to well
- 3-wire: 3 conductors + ground
- 2-wire: 2 conductors + ground
Control Box Failure Symptoms
Pump Won't Start
- No response when switch calls
- Check for power to box first
- Could be capacitor or relay
Humming/Buzzing
- Motor getting power but not starting
- Bad start capacitor likely
- Turn off quickly to prevent damage
Pump Starts Then Stops
- Overload tripping
- Could be control box or pump
- Check amp draw
Breaker Trips Immediately
- Could be shorted capacitor
- Or grounded motor
- Test control box first
Clicking from Box
- Relay chattering
- Low voltage
- Bad relay contacts
Burning Smell
- Capacitor or relay burning
- Turn off immediately
- Replace box
Troubleshooting
Safety First
- Turn off breaker before opening
- Capacitors hold charge—discharge before touching
- Use insulated tools
- Know what you're doing or call pro
Basic Checks
- Verify power to control box
- Check voltage at box terminals
- Look for burned components
- Smell for burning
Capacitor Testing
- Use multimeter with capacitance function
- Compare reading to rating on capacitor
- Weak = won't start pump
- Shorted = trips breaker
Relay Testing
- Check for burnt contacts
- Test continuity through contacts
- Listen for clicking when power applied
When to Replace Whole Box
- Multiple component failures
- Burnt/damaged housing
- Old box (easier than parts)
- Cost similar to individual parts
Replacement Cost
| Item | Cost Range |
|---|---|
| Capacitor only | $20-$50 |
| Relay only | $30-$80 |
| Complete control box | $50-$200 |
| Labor to install | $75-$150 |
Much cheaper than pulling pump!
Frequently Asked Questions
What does a well pump control box do?
Contains start capacitor and relay for 3-wire pumps. Provides extra power to start motor. Located above ground for easy service.
How do I know if my control box is bad?
Symptoms: pump won't start, humming, tripping breaker, burning smell. Test capacitor and relay with multimeter.
Do all well pumps have a control box?
Only 3-wire systems. 2-wire pumps have controls built into motor (no box above ground).
Can I replace the control box myself?
If you're comfortable with electrical work, yes. Turn off power, match replacement to pump HP. Or call a professional.
Which is better, 2-wire or 3-wire?
3-wire is easier/cheaper to repair. Most 3/4 HP+ pumps are 3-wire. 2-wire is simpler installation but harder to fix.
Control Box Problems?
We diagnose and replace control boxes quickly—no need to pull your pump.