How To Know If A Well Pump Is Bad: Diagnostic Guide & Field Test Procedures

A failing well pump typically manifests through surging water pressure, audible continuous cycling, sputtering faucets, or a complete loss of water delivery. Diagnosing the issue requires evaluating the pressure tank drawdown cycle, checking the electrical resistance and amperage at the pressure switch, and testing the motor control box capacitors.

Diagnostic Preparation and Electrical Safety Setup

Accurately diagnosing a residential submersible or jet well pump requires a systematic approach to isolate mechanical, electrical, and hydraulic faults before pulling equipment from the casing. Working with residential water systems involves high voltages (230V circuits) and heavy rotating equipment, requiring strict adherence to electrical safety protocols and the use of calibrated diagnostic tools.

• Essential Gear, Tools, and Materials:
  
  
  • Digital Multimeter capable of measuring AC/DC voltage, continuity, and ohms of resistance.
  • Clamp-on Ammeter for measuring running and locked-rotor amperage.
  • 0-100 PSI Pressure Gauge with a standard hose bib attachment.
  • Insulated screwdrivers, wire strippers, and personal protective equipment including safety glasses and rubber-soled footwear.
• Mandatory Prerequisite Knowledge and Standards:
  
  
  • Familiarity with National Electrical Code (NEC) standards for pump installations.
  • Understanding of standard residential pressure switch parameters, typically pre-set to 30/50 PSI or 40/60 PSI differentials.
  • Knowledge of basic Ohm's Law calculations to interpret multimeter resistance readings against manufacturer specifications.
• Estimated Budget and Duration Benchmarks:
  
  
  • Diagnostic workflow duration: 45 to 90 minutes.
  • Estimated cost of basic diagnostic tools if purchased new: $50 to $150.
  • Professional pump replacement cost variance (if failure is confirmed): $1,500 to $3,500 depending on depth and horsepower.

Step-by-Step Well Pump Diagnostic Workflow

Step 1: Inspect the Pressure Tank and Pressure Switch Operation

Begin your diagnosis at the pressure tank and pressure switch, as these components frequently mimic down-hole pump failures. Locate the pressure switch, remove the protective cover, and observe the contacts while running water until the system calls for a pump cycle.

Warning: Line voltage is present inside the pressure switch enclosure. Do not touch exposed terminals with bare hands. Switch off the main breaker before performing resistance or wiring checks.

1. Turn on a downstream faucet and let the water run until the pressure drops and the switch points snap closed, engaging the pump.
2. Measure the exact cut-in pressure (when the pump starts) and cut-out pressure (when the pump stops) using a calibrated gauge attached to the nearby boiler drain.
3. Inspect the pressure switch contacts for pitting, burning, or insect debris that could prevent electrical continuity.
4. Check the pressure tank air pre-charge when the system is completely drained of water; the tank bladder pressure should read exactly 2 PSI below the cut-in pressure (e.g., 28 PSI for a 30/50 switch). If water sprays from the Schrader valve, the internal bladder has ruptured, requiring tank replacement.

Step 2: Perform Electrical Testing at the Control Box or Pressure Switch

If the pump fails to start when system pressure drops below the cut-in threshold, the fault may lie in the power supply, control box, pressure switch, or motor windings.

1. Use a digital multimeter set to AC voltage to verify that line power is actively supplying the pressure switch and, if applicable, the exterior control box.
2. Disconnect power at the main breaker, isolate the pump motor leads, and test the motor winding resistance using the ohm setting on your multimeter.
3. Compare your resistance measurements against the manufacturer's operational data sheet for your specific pump model horsepower and voltage rating.
4. If you measure zero resistance (short circuit) or infinite resistance (open winding/burned-out motor), the down-hole pump motor has failed and must be pulled.

Step 3: Evaluate Amperage Draw and Running Performance

When a pump runs continuously without building tank pressure or trips the thermal overload breaker intermittently, you must measure the operating amperage draw.

1. Energize the system and clamp your digital ammeter around one of the hot wire conductors supplying the pump motor.
2. Compare the running amperage reading against the Service Factor Amps (SFA) rating stamped on the pump motor or control box specification plate.
3. If the observed amperage exceeds the SFA rating, the pump is experiencing a mechanical bind, sand lock, or failing bearings, which will soon trip the thermal overload protector.
4. If the amperage is significantly lower than the rated normal operating amperage, the pump is likely running dry ("cavitating") due to a dropped water table or a sheared pump shaft.

Step 4: Check for Water Delivery Issues and Check Valve Failure

Hydraulic delivery symptoms often point directly to check valve degradation, foot valve failure, or a compromised drop pipe rather than an absolute motor failure.

1. Listen closely to the wellhead or pressure tank immediately after the pump shuts off to determine if water is immediately flowing backward through a stuck check valve.
2. Monitor the faucet for rhythmic sputtering, which indicates air is being drawn into the suction line or drop pipe due to casing cracks or a leaking pitless adapter.
3. Perform a flow-rate bucket test by timing how long it takes to fill a five-gallon container and converting the result to gallons per minute (GPM), then comparing it to your well's original yield test report.

Well Pump Diagnostic Parameter Matrix

Common Well System Failures and Field Remedies

• Short-Cycling (Pump rapid-fires on and off every few seconds):
  
  
  • Root Cause: Waterlogged pressure tank where the air pre-charge has escaped or the internal bladder has failed, eliminating the cushion needed to absorb water expansion.
  • Actionable Fix: Drain the entire water system, check and reset the air pre-charge to 2 PSI below cut-in pressure, or replace the pressure tank if the bladder is ruptured.
• Pump Runs Continuously Without Shutting Off:
  
  
  • Root Cause: A severed drop pipe, a stuck check valve allowing water to drain back into the well, a severe underground line leak, or a lowered water table causing pump cavitation.
  • Actionable Fix: Isolate the house plumbing by closing the main shut-off valve after the pressure tank; if the pump still runs continuously, the issue is down-hole or at the check valve.
• Complete Loss of Water with No Pump Sound:
  
  
  • Root Cause: Tripped thermal overload breaker, blown control box capacitor, burnt-out pressure switch, or complete electrical failure of the motor windings.
  • Actionable Fix: Reset the circuit breaker, test voltage across the pressure switch contacts, inspect control box start/run capacitors for bulging or leaking dielectric fluid, and replace failed electrical components.
• Sputtering Faucets and Pumping Air:
  
  
  • Root Cause: Drawdown of the well water level below the pump intake level during peak usage, or a microscopic crack in the PVC drop pipe sucking air into the system.
  • Actionable Fix: Throttle back the downstream flow valve to match the restricted well recovery yield, or hire a contractor to lower the pump deeper into the casing.

Frequently Asked Questions

How long does a typical submersible well pump last?

A high-quality residential submersible well pump typically lasts between 8 to 15 years, depending heavily on water chemistry (iron, hard water, sediment), frequency of cycling, and proper sizing of the pressure tank. Maintaining correct pressure tank air pre-charge prevents premature motor burnout caused by excessive short-cycling.

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

Yes, the vast majority of electrical and pressure diagnostics can be completed above ground without pulling the pump. By testing voltage, resistance, amperage at the pressure switch or control box, and evaluating pressure tank behavior, you can accurately isolate electrical faults and switch failures.

What causes a well pump to burn out?

Well pumps commonly burn out due to continuous running caused by water leaks, rapid short-cycling from a waterlogged tank, low voltage conditions from the utility provider, or running dry when the well's water table drops below the pump intake. Installing a low-water cutoff switch is an effective preventative measure against dry-run failures.

How do I know if my well pump check valve is bad?

If your pump cycles on for short bursts even when no water is being used in the house, or if you experience a significant delay in water delivery followed by sputtering when you turn on a faucet, the check valve is likely failing. A faulty check valve allows pressurized water to drain backward through the pump and back down into the well casing.

Ensure the long-term reliability of your water system by scheduling a professional inspection if your well pump exhibits persistent electrical overloads or unexplainable pressure drops. Contact our certified technicians today to diagnose, repair, or replace your failing well pump equipment with minimal downtime.