Submersible Pump Problems and Troubleshooting
No water, falling flow, an overload relay that keeps tripping, a burnt motor winding. The most common submersible pump problems and motor faults, how to recognise them and how to fix them.
Safety first
Before you start troubleshooting
Every check on the control panel and motor must be carried out with the power isolated and by a qualified electrician. This guide lists possible causes; for measured values, always refer to the motor nameplate and datasheet. If the same failure keeps recurring, find the cause before replacing parts: otherwise the new pump or motor will fail the same way.
The pump runs but delivers no water
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Water level has dropped below the pump intake | Water flows briefly and then stops, current is low | Check the setting depth against the dynamic water level; fit dry-run protection and match the flow to the well yield |
| Motor is running in reverse | Little water, pressure lower than expected | Swap two of the three phases and compare the pressure; the direction giving higher pressure is correct |
| Non-return valve fitted backwards or stuck | Pump runs, no flow at the outlet | Check the valve direction and that it opens and closes freely |
| Broken rising main or major leak | Pressure does not build, weak flow at the well head | Pull the pump and inspect the pipe joints |
| Coupling or shaft failure between motor and pump | Motor draws normal current but no water at all | Pull the pump and check the shaft coupling; the shaft should turn freely by hand |
Flow and pressure have dropped over time
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Sand wear on impellers and diffusers | Sandy well, slow and steady loss of performance | Replace worn parts; reduce sand using the steps in the sand guide |
| Deposits on the intake strainer or hydraulic surfaces | Water high in iron or manganese | Pull and clean the pump; plan periodic cleaning |
| Dynamic water level has fallen | Seasonal decline or neighbouring wells | Measure the level; lower the pump or reduce the flow if necessary |
| Leak in the pipeline | Pump performance normal but less water reaches the delivery point | Inspect the surface pipeline and connections |
| Low voltage or wrong frequency | Low motor speed, high current | Measure the voltage at the motor supply while running |
| Motor running in reverse (after new installation or maintenance) | Performance low from the start | Check the direction of rotation |
The overload relay keeps tripping
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Low or unbalanced supply voltage | Current differs between phases, voltage below nameplate | Measure voltage and phase balance; use an under/overvoltage relay |
| Phase loss | Motor hums, current zero on one phase | Check fuses, contactor and cable splices; fit a phase failure relay |
| Pump strained or jammed by sand | Very high current at start | Pull and clean the pump; if the shaft does not turn by hand, do not keep attempting to start |
| Overload relay set incorrectly | Current below nameplate but the relay trips | Set the relay to the motor rated current |
| Cable cross-section too small | Voltage drops noticeably at start | Recalculate the cable for the installed depth; see the cable sizing guide |
| Pump running at very low head and very high flow | Valve fully open, high current | Check the duty point; throttle the flow with a valve or review the pump selection |
The motor does not start at all
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| No power or blown fuse | No voltage at the panel | Check the supply, fuses and contactor |
| Protection relay has tripped | Dry-run or phase relay showing a fault | Find why the relay tripped; check water level and phase condition |
| Cable or splice failure | No continuity on one or more phases | Measure cable continuity and check the splices |
| Winding or insulation failure | Insulation resistance below the minimum stated by the motor manufacturer | Pull the motor; identify the cause of the burnout before rewinding |
| Pump jammed by sand | High current at start, motor does not turn | Pull and clean the pump |
The pump starts and stops too often
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Pressure switch or pressure tank set incorrectly | Switches on and off at short intervals | Check the switch settings and tank pre-charge pressure |
| Well yield lower than pump flow | Dry-run protection trips frequently | Reduce the flow, extend running time or add storage |
| Non-return valve leaking | Pressure falls quickly after the pump stops | Inspect or replace the non-return valve |
The motor winding keeps burning out
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Insufficient cooling | Wide casing or pump set below the screen | Calculate the annular velocity; fit a flow sleeve if needed |
| Voltage drop | Long cable, voltage dips at start | Size the cable for the installed depth |
| Phase loss or imbalance | Unstable supply | Use a phase failure relay |
| Too many starts | Many starts and stops per hour | Review the control system and tank volume |
| Dry running | Water level occasionally falls below the intake | Fit dry-run protection |
Most recurring winding failures are caused by installation decisions, not manufacturing faults. See the motor cooling guide for details.
Noise, vibration or sand in the water
| Possible cause | How to recognise it | Remedy |
|---|---|---|
| Water level low, pump drawing air | Intermittent flow, aerated water | Lower the pump or reduce the flow |
| Bearing wear | Increasing noise and vibration, sandy well | Pull the pump and inspect the bearings |
| Well not properly developed | Sand in the water continuously | Have the well developed by your driller; reduce flow, use a sand separator |
| Flow too high for the well yield | Excessive drawdown, more sand at each start | Match the flow to the well yield; use soft starting |
Six rules that prevent most failures
Size on the dynamic water level
A pump sized on the static level ends up undersized and close to dry running.
Fit complete protection
Overload, dry-run and phase failure protection prevent the majority of failures.
Size the cable for the depth
The cable must be sized for the total length, not only for the motor rating.
Check motor cooling
Use a flow sleeve in wide casings and when the pump is set below the screen.
Commission correctly
Check the direction of rotation and record the first readings; see the installation guide.
Record readings regularly
Logging current, voltage, flow and pressure periodically reveals problems before they become failures.
Frequently asked questions
Will a submersible pump deliver water if it runs in reverse?
Usually it delivers some water, but pressure and flow are noticeably lower, which is why reverse rotation often goes unnoticed. Check the direction of rotation after every new installation and every electrical service.
What happens if a submersible pump runs dry?
The water-filled motor and the pump bearings rely on water for cooling and lubrication. Dry running can quickly damage the bearings and the motor. Dry-run protection eliminates this risk.
What should I do when the motor winding burns out?
First identify the cause: voltage, phase loss, cooling, sand or dry running. FANPO motors are rewindable, but a motor rewound without removing the cause will fail the same way.
Why does the overload relay keep tripping?
The most common causes are low or unbalanced voltage, phase loss, sand strain, an undersized cable and an incorrect relay setting. Measuring current and voltage on all three phases while running usually reveals the cause.
What information should I send FANPO for troubleshooting?
Send the pump and motor model, setting depth, dynamic water level, cable length and cross-section, running current and voltage, and a short description of the symptom through the contact page.
Prepared by the FANPO engineering team · Last updated: 8 November 2026