How To Tell If Well Pump Is Bad: Professional Diagnostic And Troubleshooting Guide
To determine if a well pump is failing, you must evaluate the system's ability to maintain a standard 30/50 or 40/60 PSI range, check for electrical continuity across the motor windings, and monitor for short-cycling. A definitive diagnosis requires verifying that the pressure switch is receiving 230V (or 115V) power and confirming that the pump’s amperage draw matches the manufacturer’s nameplate specifications during operation.
Pre-Diagnostic Checklist and Equipment Requirements
Diagnosing a well pump requires a systematic approach to differentiate between electrical failure, mechanical wear, and plumbing leaks. Before opening the well cap or the pressure switch cover, ensure you have organized the necessary diagnostic tools and understand the safety protocols regarding high-voltage electrical components. Most residential well systems operate on a 230V double-pole circuit, which can be lethal if handled improperly.
Essential Diagnostic Tools and Benchmarks
- Digital Multimeter: Capable of measuring AC Voltage, Amperage (with a clamp-on feature), and Resistance (Ohms).
- Schrader Valve Pressure Gauge: To check the air pre-charge in the pressure tank.
- Standard Screwdrivers and Nut Drivers: For removing the pressure switch cover and wire terminals.
- Well Seal/Cap Tools: A socket set or pipe wrench if access to the pitless adapter or wellhead is required.
- Standard Timeframe: A comprehensive diagnostic takes 45 to 90 minutes.
- Expected Life Cycle: Submersible pumps typically last 12–15 years, while jet pumps average 10 years; if your unit exceeds these benchmarks, mechanical fatigue is the likely culprit.
Systemic Workflow for Identifying Well Pump Failure
Step 1: Verify Electrical Integrity and Power Supply
Before assuming the pump motor has burned out, you must confirm that electricity is reaching the system. Start at the main service panel and locate the dedicated breaker for the well pump. If the breaker has tripped, reset it once. If it trips immediately again, you have a direct short in the motor windings or the submerged power cable.
If the breaker is on, move to the pressure switch, usually located near the base of the pressure tank. Use your multimeter to check for voltage on the "line" side (incoming power) and the "load" side (power going to the pump). If the switch points are closed but no power is passing through to the load side, the pressure switch has failed—a $30 fix that is often mistaken for a $2,000 pump failure.
Warning: Always exercise extreme caution when testing live terminals. Ensure your multimeter leads are properly seated and your hands are clear of any grounded metal surfaces.
Step 2: Analyze Pressure Tank and Short-Cycling Patterns
A pump that turns on and off rapidly—every few seconds when water is running—is "short-cycling." This is rarely a sign of a bad pump initially, but it is the leading cause of pump motor burnout. Short-cycling is almost always caused by a waterlogged pressure tank.
To test this, turn off the power to the pump and drain the system by opening a nearby faucet until the water stops. Use a tire gauge to check the air valve at the top of the tank. The air pressure should be exactly 2 PSI below the "cut-in" pressure of your switch. If your switch is set to 30/50 PSI, the tank needs 28 PSI of air. If water squirts out of the air valve, the internal bladder has ruptured, and the tank must be replaced to prevent the pump from burning out.
Step 3: Monitor Flow Rate and System "Spitting"
If you notice air bubbles or "spitting" from your faucets, the system is drawing air. This typically indicates one of three failures:
- Low Water Table: The well is temporarily exhausted, and the pump is sucking air.
- Broken Drop Pipe: The pipe connecting the submersible pump to the surface has a hole or crack, allowing air to mix with the water column.
- Failed Check Valve: The valve is allowing water to flow back into the well, creating a vacuum that draws air into the lines.
Continuous spitting accompanied by a drop in pressure is a high-level indicator that the pump is struggling to maintain a prime or is mechanically compromised.
Step 4: Perform a Resistance (Ohm) Test on Motor Windings
For submersible pumps, you can test the motor's health from the surface without pulling the pump. Disconnect the pump wires from the pressure switch or control box. Set your multimeter to the Ohms (Ω) setting.
For a standard 3-wire pump, measure the resistance between the Black and Yellow wires (Main winding) and the Red and Yellow wires (Start winding).
- Normal Readings: Most 1/2 HP to 1 HP pumps should show between 1.0 and 5.0 ohms for the main winding.
- Failed Readings: A reading of "OL" (Open Line) indicates a broken wire or a burned-out winding. A reading of 0 ohms indicates a direct short.
- Ground Test: Measure between each wire and the green ground wire. Any reading other than "OL" indicates the motor insulation has failed and electricity is leaking into the well water.
Step 5: Test Amperage Draw Under Load
If the pump is running but providing low pressure, use a clamp-on ammeter around one of the hot wires while the pump is active. Compare this reading to the "Service Factor Amps" (SFA) listed on the pump’s control box or nameplate.
- High Amperage: Indicates the motor is working too hard due to a failing bearing or a clogged impeller.
- Low Amperage: Often indicates the pump has broken free of the shaft or the well has run dry, meaning the motor is spinning with no resistance from water.
Pro-Tip: If the amperage is normal but you have no water, the problem is likely a physical blockage in the intake screen or a snapped drive shaft, rather than an electrical failure.
Pressure Tank vs Well Pump: Which Is the Problem?
Well System Component Performance Standards
| Component | Normal Operating Range | Failure Indicator | Primary Resolution |
|---|---|---|---|
| Pressure Switch | 30/50 or 40/60 PSI | Burnt contacts; no "click" | Replace switch / Clean contacts |
| Pressure Tank | 2 PSI below cut-in | Water at air valve; heavy tank | Replace bladder or tank assembly |
| Motor Windings | 0.5 - 20.0 Ohms (varies) | "OL" or 0.00 Ohms | Pull and replace pump motor |
| Amperage Draw | Within 10% of SFA rating | 25%+ above SFA rating | Check for pump sand-locking |
| Voltage Drop | Less than 3% from source | >5% drop during startup | Upgrade wire gauge or check source |
| Cycle Frequency | < 6 starts per hour | > 20 starts per hour | Check tank pre-charge/bladder |
Common Well Failures and Field Remedies
Motor Hum with No Rotation
- Root Cause: The startup capacitor in the control box has failed, or the pump impeller is "sand-locked" by debris.
- Actionable Fix: Replace the start capacitor if you have a 3-wire system. For 2-wire systems, you may need to "surge" the pump by rapidly switching the breaker or use a "hard start" kit to break the impeller loose.
Pump Runs Continuously Without Reaching Cut-off
- Root Cause: A leak in the drop pipe below ground or a severely worn impeller that can no longer generate sufficient centrifugal force to reach the 50 or 60 PSI limit.
- Actionable Fix: Close the main valve to the house. If the pump still won't reach cut-off, the leak is in the well or the pump is mechanically dead. If it does reach cut-off, the leak is inside the house or the service line.
Frequent Thermal Overload Tripping
- Root Cause: The pump motor is overheating due to low voltage, a restricted cooling flow (shroud issues), or internal bearing friction.
- Actionable Fix: Verify voltage at the wellhead is within 10% of the rating. If voltage is correct, the motor is near the end of its service life and requires replacement.
Sediment and Cloudiness in Water
- Root Cause: The pump is positioned too low in the well or the well screen has collapsed, causing the pump to ingest silt which grinds down the impellers.
- Actionable Fix: Measure the well depth and raise the pump 5–10 feet if possible. Install a spin-down sediment filter before the pressure tank to protect the plumbing.
Frequently Asked Questions
How many years does a typical well pump last?
A high-quality submersible well pump generally lasts between 12 and 15 years, though factors like water quality (acidity and mineral content) and the frequency of "starts" can shorten this lifespan. Jet pumps located above ground typically have a shorter lifespan of 10 years due to the mechanical stress of maintaining a prime.
Why is my well pump running but I have no water?
This is usually caused by a broken connection at the pitless adapter, a snapped drive shaft in the pump, or the water table dropping below the pump intake. If the pump is a jet pump, it may simply have lost its prime due to a minor leak in the suction line.
Can a bad pressure tank look like a bad well pump?
Yes, a waterlogged pressure tank causes the pump to cycle on and off every few seconds. This constant "short-cycling" mimics the behavior of a failing pump and, if left unaddressed, will actually destroy the pump motor's start windings within a matter of weeks.
How much does it cost to replace a well pump?
On average, a professional well pump replacement costs between $1,500 and $2,500. This includes the cost of a new 1/2 HP or 3/4 HP submersible pump, labor to pull the old unit from the well, and new wiring/shrink-wrap kits to ensure a watertight electrical connection.
Is it possible to fix a well pump without pulling it?
You can fix the control box, the pressure switch, and the pressure tank without pulling the pump. However, if the diagnostic tests show a direct short in the motor windings or a mechanical failure of the impellers, the pump must be pulled from the well for replacement.
Ensuring Long-Term Well System Reliability
Maintaining a consistent diagnostic schedule and replacing your pressure tank at the first sign of bladder failure can double the lifespan of your well pump. If your system requires professional intervention, ensure your technician performs a full amperage and drawdown test to verify the health of the entire water system.
