Well Pump Control Box Troubleshooting Guide

What's Inside a Control Box

3-Wire vs 2-Wire Systems

• 3-Wire: Has control box above ground
• 2-Wire: All components in motor (underwater)
• This guide is for 3-wire systems only

Components

• Start capacitor: Provides boost to start motor
• Run capacitor: Keeps motor running efficiently
• Relay: Switches start capacitor in/out of circuit
• Overload protector: May be included (trips on overcurrent)
• Terminal connections: Wire connections to pump

How It Works

1. Power comes from pressure switch
2. Relay energizes start capacitor
3. Motor starts with extra boost
4. Relay disconnects start capacitor
5. Motor runs on run capacitor (if equipped)

Failure Symptoms

Pump Won't Start at All

• No sound, no response
• Check power to box first
• May be relay or capacitor
• Or wiring connection

Pump Hums But Won't Run

• Motor trying but can't start
• Usually start capacitor
• Could be relay not engaging

Breaker Trips Immediately

• Short circuit in box
• Or motor problem (not box)
• Check for burned wires

Pump Starts Then Stops

• Overload tripping
• Run capacitor issue
• Or motor overheating

Rapid Cycling

• Usually pressure tank issue
• But relay could be sticking

Burning Smell

• Something has failed/burned
• Stop using immediately
• Inspect before powering on again

Diagnosis Steps

Visual Inspection

1. Power OFF at breaker
2. Remove box cover
3. Look for:
   • Burned or melted components
   • Bulging or leaking capacitors
   • Burned smell
   • Loose or corroded connections
   • Water intrusion

Capacitor Check

• Visual: bulging, leaking, or cracked = bad
• Meter test: check microfarads (µF)
• Should be within 10% of rated value
• Reading 0 or very low = failed

Relay Check

• Look for burned contacts
• Should click when energized
• Test continuity through contacts

Wiring Check

• All connections tight?
• Any corrosion?
• Wire insulation intact?

Repairs

Replacing Capacitors

• Match µF rating exactly
• Match or exceed voltage rating
• Note wire positions before removing
• Discharge old capacitor first
• Cost: $20-$60 per capacitor

Replacing Relay

• Match to pump HP
• Get same type (potential relay, etc.)
• Note wire connections
• Cost: $30-$80

Tightening Connections

• Loose connections cause heat buildup
• Clean corrosion with contact cleaner
• Ensure tight connection

DIY vs Professional

• Comfortable with electrical: DIY possible
• Not sure: call a professional
• If multiple components failed: consider replacing entire box

Whole Box Replacement

When to Replace Whole Box

• Multiple failed components
• Extensive damage or burning
• Water intrusion damage
• Very old box
• Can't identify problem

Matching the Box

• Must match pump HP
• Must match voltage (usually 230V)
• Match wire count/connections
• Bring old box to supplier if unsure

Cost

• Control box: $100-$250
• Professional installation: $50-$150
• Total: $150-$400

Installation

1. Power OFF
2. Label all wires
3. Remove old box
4. Mount new box
5. Connect wires to matching terminals
6. Close box, restore power
7. Test operation

We service all major pump brands including Franklin Electric, Grundfos, Goulds (Xylem), and Sta-Rite (Pentair). Our trucks carry common parts and components for same-day repairs.

Frequently Asked Questions

What does a well pump control box do?

Contains capacitors and relay for 3-wire submersible pumps. Provides starting power boost and manages electrical supply to motor.

How do I know if my control box is bad?

Pump won't start, hums, trips breaker, or cycles rapidly. Open box (power off) and check for burned components, bulging capacitors, or burnt smell.

Can I replace just the capacitor?

Yes—often the capacitor is the only failed component. Match µF and voltage ratings. Cost: $20-$60.

Do 2-wire pumps have a control box?

No—2-wire pumps have the starting components inside the motor (underwater). If a 2-wire pump fails, the pump usually needs replacement.

How long does a control box last?

Typically 10-20+ years. Capacitors often fail first. Lightning strikes can damage boxes prematurely.