Systematic Troubleshooting: Start With the Symptoms
When a submersible pump stops working correctly, resist the urge to immediately pull it from the well. Over 40% of reported submersible pump failures turn out to be surface equipment problems — electrical, control, or piping issues that never required retrieving the pump. This guide walks through a systematic diagnostic process from the surface down.
Symptom 1: Pump Does Not Start
| Possible Cause | Diagnostic Test | Solution |
|---|---|---|
| Tripped circuit breaker | Check breaker position, measure voltage at panel | Reset once. If trips again, do NOT reset — investigate cause |
| Blown fuse | Visual inspection or continuity test | Replace with correct rating. Never use higher amp fuse |
| Overload relay tripped | Check overload indicator on control panel | Allow motor to cool, reset. Investigate cause of overload |
| Low voltage supply | Measure voltage at controller input (must be +/-10% nameplate) | Check transformer tap settings or utility supply |
| Open motor winding | Resistance test: each phase to ground, phase to phase | If open circuit, pump must be pulled and motor replaced |
| Shorted cable or motor | Megger test: less than 1 megohm to ground = fault | Isolate cable from motor at wellhead to determine location |
| Control circuit failure | Jump pressure switch or level control to test | Replace faulty control component |
Diagnostic Flow for No-Start Condition
- Check power at source: Is there voltage at the circuit breaker output? Yes → go to 2. No → utility or breaker problem.
- Check power at controller: Is voltage present at the controller input terminals? Yes → go to 3. No → wiring problem between panel and controller.
- Jump control circuit: Bypass pressure switch/level control. Does pump start? Yes → control switch faulty. No → go to 4.
- Measure at motor leads: With controller calling for pump, is voltage at motor leads correct? Yes → motor or cable fault underground. No → controller/output relay fault.
Symptom 2: Pump Runs But Delivers Low Flow or Pressure
| Possible Cause | Diagnostic Test | Solution |
|---|---|---|
| Clogged suction screen | Check pressure differential across screen (if accessible) | Clean screen; consider larger screen area or pre-filter |
| Worn impeller / wear rings | Compare flow/pressure against original pump curve | Pull pump, replace worn components |
| Reverse rotation (3-phase) | Swap any two power leads, observe flow change | If flow increases ~50%, rotation was reversed — correct wiring |
| Low water level / drawdown | Measure pumping water level, compare with pump setting depth | Lower pump or reduce flow rate |
| Leaking discharge pipe | Look for wet spots or pressure drop along buried pipe | Excavate and repair pipe |
| Partially closed valve | Physically verify all valves are fully open | Open valve fully; replace if stem is sheared |
| Check valve stuck partially closed | Measure pressure above and below check valve | Replace check valve |
Symptom 3: Pump Trips Overload or Circuit Breaker
- Overload setting too low: Verify that the overload relay is set to the motor nameplate full-load amps (FLA), not an arbitrary lower value.
- Voltage imbalance (3-phase): Calculate percent imbalance: V_imbalance = (max deviation from average / average voltage) x 100. More than 2% imbalance can cause 15%+ current increase in one phase.
- Mechanical binding: Disconnect pump from power and try to rotate shaft manually (if accessible). High resistance = mechanical problem requiring pump removal.
- Debris in pump: Sand or gravel in the impeller increases amp draw. If the well is producing sand, consider a sand separator or pump with higher abrasion resistance.
- Undersized wiring: Voltage drop in the drop cable causes increased current draw. Verify cable size against the installation's depth and motor horsepower.
Symptom 4: Noisy Operation or Vibration
- Cavitation: A sound like gravel passing through the pump indicates cavitation — vapor bubbles forming and collapsing in the pump. Caused by insufficient NPSH (too much suction lift, clogged strainer, or throttled suction valve). Cavitation will destroy impellers rapidly.
- Worn bearings: A high-pitched whine or grinding sound in surface motors. In submersible motors, bearing noise is only detectable through vibration analysis at the wellhead.
- Pipe vibration / water hammer: Thumping or banging when the pump starts or stops. Install a pressure tank or surge arrestor to absorb water hammer.
- Loose mounting: Check that all mounting bolts, pipe clamps, and support brackets are tight.
When to Pull the Pump
If surface diagnostics do not resolve the issue and the following conditions are met, it is time to retrieve the pump:
- Motor windings show open circuit or short to ground
- Insulation resistance below 0.5 megohms and not recovering after drying
- Flow rate less than 70% of original with no surface cause identified
- Mechanical binding confirmed (pump shaft cannot rotate)
- Sand production from the well has become excessive
Need diagnostic support? NOVAPUMP's technical team can help you interpret electrical test results and advise whether pump retrieval is necessary before you incur the cost.