How To Check A Well Pump: The Complete Diagnostic Guide

Diagnosing a failing well pump requires a systematic evaluation of electrical continuity, pressure switch functionality, and hydraulic performance using a digital multimeter and pressure gauge. By isolating electrical faults from mechanical blockages, homeowners and technicians can pinpoint system failures safely and efficiently without unnecessary component replacements.

Pre-Operation & Equipment Safety Checklist

Troubleshooting an operational residential water well system demands rigorous adherence to electrical safety protocols and mechanical inspection standards. Before opening control boxes or checking pressure tanks, verify that you have assembled the correct diagnostic gear to prevent electrical shock and equipment damage.

• Essential Gear & Tools: True RMS digital multimeter (capable of measuring AC/DC voltage, ohms, and microfarads), non-contact voltage tester, tongue-and-groove pliers, standard screwdrivers, insulated wire strippers, and a calibrated 0-100 PSI water pressure gauge with a hose bib adapter.
• Mandatory Prerequisite Knowledge: Familiarity with National Electrical Code (NEC) standards for residential well wiring, understanding of single-phase 230V and 115V circuits, and recognition of standard pressure switch cut-in/cut-out thresholds (typically 30/50 or 40/60 PSI).
• Time & Budget Benchmarks: Diagnostic procedures typically take 45 to 90 minutes. Professional service calls range from 150 to 400 USD, while DIY multimeter testing requires zero material cost beyond the initial tool investment.

Step-by-Step Well Pump Troubleshooting Workflow

Step 1: Inspect the Pressure Tank and Pressure Switch

Begin your assessment at the pressure tank and pressure switch assembly, as these components dictate when the well pump cycles on and off. Turn off power to the pump at the main circuit breaker before removing the plastic cover of the pressure switch to inspect the contact points.

1. Look for burnt, pitted, or corroded electrical contacts inside the pressure switch box, which frequently prevent electrical current from reaching the pump motor.
2. Use a thin piece of fine-grit sandpaper or a contact file to clean debris from the contact points if pitting is minimal.
3. Check the pressure tank pre-charge by draining the entire system of water (turn off power, open the lowest faucet until flow stops, and leave it open).
4. Measure the air valve (Schrader valve) on top of the pressure tank using a standard tire pressure gauge; the pre-charge pressure must read exactly 2 PSI below your pressure switch cut-in setting (e.g., 28 PSI for a 30/50 switch).

Warning: Never service a pressure switch or control box without first verifying power is completely disconnected using a non-contact voltage tester. Live 230V circuits present severe electrocution hazards.

Step 2: Test Electrical Voltage at the Pressure Switch

Restore power to the well pump circuit at the main breaker panel to test whether electricity is successfully flowing through the pressure switch to the pump.

1. Set your digital multimeter to measure AC Voltage (ranging up to 300V or higher).
2. Carefully place the multimeter probes across the incoming power terminals (line side) of the pressure switch; you should read approximately 230 volts for a standard heavy-duty pump (or 115 volts for shallower systems).
3. Manually close the pressure switch contacts using an insulated tool or allow system pressure to drop until the switch engages, then test the outgoing terminals (load side).
4. If voltage registers on the incoming side but drops to zero on the outgoing side when the contacts close, the pressure switch is defective and must be replaced.

Pro-Tip: If ants or insects are nesting inside the pressure switch housing—a common cause of electrical failure—seal the wire entry knockouts with silicone after clearing the debris.

Step 3: Measure Motor Resistance and Amp Draw at the Control Box

If your system utilizes a 3-wire submersible pump or a 2-wire setup with an external control box, you must test the motor windings for shorts, opens, or grounds.

1. Disconnect all power to the control box and discharge any capacitors safely using an insulated screwdriver.
2. Disconnect the motor wires (Yellow, Red, Black) from the control box terminals.
3. Set your multimeter to the ohms (resistance) setting and measure resistance between the Black and Yellow wires, Black and Red wires, and Yellow and Red wires.
4. Consult the manufacturer specifications for your specific pump horsepower; recorded resistance values that deviate more than 10% from factory specs indicate damaged windings or a burned-out motor.
5. Test for a grounded winding by touching one multimeter probe to a bare ground wire or metal well casing and the other probe to each motor wire individually; any reading other than infinite resistance (OL) means the motor has shorted to ground.

Step 4: Evaluate Pump Performance Using a Pressure Gauge

Verify the hydraulic performance of the pump by attaching your water pressure gauge to an outdoor spigot located as close to the pressure tank as possible.

1. Run water from a nearby faucet to force the pump to kick on, then close all faucets to let the system fill and shut off.
2. Observe the exact pressure reading on your gauge when the pump turns on (cut-in pressure) and when it turns off (cut-out pressure).
3. If the pump runs continuously without ever reaching the cut-out pressure threshold, you likely have a water-logged pressure tank, a sheared pump impeller, a drop pipe leak, or a depleted well yield.

Well Pump System Diagnostic Parameters

Common Site Failures & Field Fixes

• Root Cause: The pressure switch chatters rapidly or hums without starting the pump.
  
  
  • Actionable Fix: Inspect the small copper tube or nipple leading into the pressure switch base. Mineral scale or iron bacteria frequently clogs this port, preventing the switch from sensing accurate line pressure; clear the blockage using a piece of stiff wire.
• Root Cause: The thermal overload protector keeps tripping immediately after the pump starts.
  
  
  • Actionable Fix: Check for low voltage supply from the utility transformer or measure operating amp draw against the motor nameplate rating. A failing control box start capacitor or a jammed pump wet end will cause excessive amp draw and trip the thermal breaker.
• Root Cause: The pump cycles on and off rapidly every few seconds when running a faucet (known as water hammer or rapid cycling).
  
  
  • Actionable Fix: The pressure tank has lost its air cushion due to a failed bladder or air loss. Drain the tank completely and re-inflate the air charge, or replace the pressure tank if the internal bladder is ruptured.
• Root Cause: Sizzling sounds or zero water delivery accompanied by a tripped circuit breaker.
  
  
  • Actionable Fix: This indicates a dry run condition or a severed drop cable. Turn off power immediately to prevent total motor burnout, verify static water table levels, and inspect wiring splices inside the wellhead sanitary seal.

Frequently Asked Questions

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

A burned-out well pump typically exhibits tripped circuit breakers, infinite or zero resistance across motor windings during multimeter testing, and a distinct electrical burning odor near the control box. If the motor fails to hum or engage when voltage is actively supplied to the leads, the internal motor is likely seized or burned out.

Why is my well pump running constantly and not building pressure?

Continuous running without pressure buildup usually points to a severed drop pipe inside the well casing, a stuck check valve, worn pump impellers, or a completely depleted well source. Turn off the system immediately to prevent dry-running damage while you inspect for visible leaks around the wellhead and pressure tank.

Can a bad pressure switch cause a well pump not to turn on?

Yes, pressure switches are prone to internal contact corrosion, insect intrusion, and mechanical spring fatigue over time. If the electrical contacts fail to close when water pressure drops below the cut-in threshold, electricity cannot reach the pump motor, resulting in a complete loss of water supply.

How long do residential well pumps typically last?

Standard submersible well pumps last between 10 to 15 years, depending on water chemistry, mineral content, and daily pumping cycles. Systems operating in environments with high iron, sulfur, or abrasive sand content may experience premature mechanical wear within 5 to 8 years.

What pressure should my well pressure tank be?

Your pressure tank air pre-charge should always be set 2 PSI below the cut-in pressure of your pressure switch. For example, a standard 30/50 PSI pressure switch requires an empty tank pre-charge of exactly 28 PSI, measured when all water pressure has been completely drained from the system.

Contact our licensed plumbing and pump specialists today to schedule comprehensive flow testing, electrical diagnostics, or emergency well pump replacement services.