How To Check A Well Pump: The Complete Diagnostic Guide

Diagnosing a failing well pump requires a systematic evaluation of electrical resistance, operational pressure, and mechanical integrity using a multimeter and pressure gauge. By isolating the pressure switch, checking the control box, and testing amperage draw, you can accurately determine whether the issue stems from the power supply, the pressure tank, or the pump motor itself.

Pre-Operation & Equipment Safety Checklist

Troubleshooting an electromechanical water delivery system involves working with high-voltage electricity and pressurized water. Before beginning any diagnostic procedures, ensure you have the proper safety gear, diagnostic instrumentation, and an understanding of residential water system architecture. A methodical approach prevents electrical shock, pump burnout, and system contamination.

• Essential Gear and Tools: Digital multimeter capable of measuring AC/DC voltage and ohms, clamp-on ammeter, 0-100 PSI pressure gauge with a hose bib adapter, insulated screwdrivers, needle-nose pliers, wire strippers, and a non-contact voltage tester.
• Mandatory Safety Gear & Standards: Safety glasses, rubber-soled footwear, and heavy-duty work gloves. Always shut off the main circuit breaker supplying the well pump and verify zero energy state before opening electrical enclosures. Follow National Electrical Code (NEC) guidelines for wet-location electrical testing.
• Time and Budget Benchmarks: Diagnostic testing typically takes 45 to 90 minutes. If replacement components such as a pressure switch or control box are required, material costs generally range from thirty to three hundred dollars.

Step-by-Step Well Pump Diagnostic Workflow

Step 1: Inspect the Power Supply and Circuit Breaker

Begin by verifying that the well pump is receiving electricity. Locate the dedicated dual-pole circuit breaker in your main electrical panel and check if it has tripped. If the breaker is tripped, do not immediately reset it, as a shorted pump motor or damaged underground wire can cause dangerous arcing.

1. Turn the circuit breaker firmly to the OFF position and then back to the ON position to reset an internal thermal trip.
2. Locate the pressure switch mounted near the pressure tank. Use your non-contact voltage tester to check for incoming power at the line terminals.
3. Check the mechanical contacts inside the pressure switch for pitting, burning, or insect infestation, which can block electrical continuity.

Warning: Line terminals inside the pressure switch carry 230 volts of electricity, which is lethal. Never touch exposed terminals with bare hands or uninsulated tools.

Step 2: Check the Pressure Tank and Air Pre-Charge

A malfunctioning pressure tank can cause short-cycling, where the pump turns on and off rapidly, eventually burning out the motor. To check the tank, you must completely drain the system of water.

1. Shut off the power to the well pump at the circuit breaker.
2. Open the lowest plumbing valve or a nearby hose bib to drain all water from the pressure tank completely. Leave the faucet open.
3. Locate the Schrader valve on top of or beside the pressure tank (similar to a car tire valve).
4. Use a standard tire pressure gauge to measure the air pressure inside the tank bladder. The air pressure should read exactly 2 PSI below the cut-in pressure of your switch (for example, 26 PSI for a standard 30/50 PSI switch).
5. If water sprays out of the Schrader valve, the internal rubber bladder has ruptured, and the entire pressure tank must be replaced.

Step 3: Test Electrical Resistance and Ohms at the Control Box

If your system utilizes a 3-wire submersible pump, it will feature an above-ground control box housing a starting capacitor and relay switch.

1. Disconnect power to the control box and remove the protective cover.
2. Discharge the capacitor using an insulated screwdriver across the terminals to prevent shock.
3. Set your multimeter to the ohms (resistance) setting to test the three motor leads: Yellow (Start), Red (Run), and Black (Common).
4. Measure resistance between Yellow and Red, Red and Black, and Black and Yellow. Add the two lower readings together; the sum should roughly equal the highest reading.
5. Check for a ground fault by testing resistance between each wire lead and the bare grounding wire or a clean metal point on the well casing. Any reading other than infinite ohms indicates a shorted motor winding or damaged drop cable.

Step 4: Measure Amperage Draw Under Load

Monitoring the operating current verifies whether the pump motor is struggling mechanically or drawing excess current due to a failing stator or a jammed impeller.

1. Restore power to the system and force the pump to turn on by draining the pressure tank until the contacts close.
2. Use a clamp-on ammeter around one of the power wires supplying the pump or pressure switch.
3. Compare your measured amperage reading against the Service Factor Amps (SFA) listed on the pump motor data plate.
4. If the measured amperage significantly exceeds the SFA rating, the motor has a locked rotor, winding failure, or is pulling against a fully blocked discharge pipe.

Well Pump Diagnostics and Parameter Specifications

Troubleshooting Common Well System Failures

• Root Cause: The pump runs continuously without building pressure or shutting off.
  
  
  • Actionable Fix: Inspect for a ruptured drop pipe inside the well casing, a stuck check valve, or a severe leak in the supply line between the well head and the residence.
• Root Cause: The system experiences rapid click-on, click-off cycling while water is running.
  
  
  • Actionable Fix: The pressure tank is water-logged due to a failed air bladder or a complete loss of air pressure. Recharge the air volume or replace the tank.
• Root Cause: Intermittent water supply where the pump cuts out unexpectedly and requires manual breaker resets.
  
  
  • Actionable Fix: Thermal overload protection is tripping due to low voltage, a failing motor running hot, or a dropping water table causing the pump to run dry.
• Root Cause: Complete loss of water with zero pump noise when faucets are opened.
  
  
  • Actionable Fix: Check for a tripped circuit breaker, a blown fuse in the control box, or a burnt-out pressure switch contact set.

Frequently Asked Questions

How do I know if my well pump is burned out?

A burned-out well pump typically exhibits infinite or zero resistance across the motor windings during a multimeter test, smells of burnt insulation, or trips the circuit breaker instantly upon startup. Additionally, if the pump hums loudly without spinning, the internal motor bearings or start capacitor may have failed.

Can I test a well pump without pulling it out of the well?

Yes, the vast majority of diagnostic work is performed above ground. You can test electrical continuity, resistance, amperage draw, pressure switch functionality, and tank air pressure at the control box, pressure switch, and pressure tank without pulling the pump drop pipe.

What causes a well pump to lose its prime?

Submersible pumps rarely lose their prime because the pump ends remain submerged beneath the water table. However, shallow-water jet pumps rely on a suction foot valve; if this foot valve degrades, debris jams the flapper, or the suction line develops a pinhole leak, water drains back down the pipe and causes a loss of prime.

How long does a standard residential well pump last?

A properly sized and installed submersible well pump typically lasts between 8 and 15 years. Lifespan is heavily influenced by water chemistry (such as high iron or acidic pH), the frequency of cycling, and whether the motor experiences frequent voltage fluctuations.

Why is my well pump pressure dropping gradually?

A gradual reduction in water pressure usually indicates mineral scaling clogging the impeller stages, a developing leak in the underground supply line, or a failing check valve allowing water to bleed backward down the well shaft. It can also signal a declining local water table or drought conditions.

Ensure your home water system operates at peak efficiency by scheduling professional evaluations if electrical anomalies persist beyond basic switch replacements. Contact our certified plumbing and well technicians today to schedule comprehensive flow testing, electrical diagnostics, or emergency pump replacement services.