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5 Causes of Submersible Pump Failure and How to Fix Them

Even with proper selection and sizing, submersible pumps can fail if they are not installed or maintained correctly. Below are five common causes of pump failure in the field—and how to address or prevent them to ensure optimal pump performance and longevity.

1. Clogging and Ragging

Cause: Wastewater and sump pumps often face debris like rags, wipes, or solids that can clog the impeller. A clogged or partially obstructed impeller forces the motor to work harder, drawing higher amperage and potentially tripping the pump on overload. A “ragged” impeller is a frequent cause of excessive current draw in sewage pumps.

Fix: If a pump is clogged, it needs to be pulled and the blockage removed manually (always follow lock-out safety procedures first).

Prevention:

• Use the correct type of pump for solids-handling, such as a non-clog, chopper, or grinder pump.
• Install screens or trash racks in the wet well to intercept large debris before it reaches the pump.
• Perform regular inspection and cleaning to prevent severe rag buildup.
• Consider retrofitting with anti-ragging impellers or cutter blades designed to combat ragging.

2. Overheating of the Motor

Cause: Submersible motors rely on the surrounding fluid to dissipate heat. If the pump runs dry or is only partially submerged, it can overheat quickly. Overheating can also occur due to overloading (pumping beyond capacity), a mechanical jam, or electrical issues causing overcurrent.

Fix: For an overheated pump, first cut power and allow it to cool. Many submersible pumps have thermal cut-outs that trip automatically on overheat—while the pump may restart when it cools, it’s essential to investigate the root cause.

Prevention:

• Maintain proper liquid levels above the pump; set the “off” float switch high enough to prevent exposure to air.
• Consider a jacketed cooling system or a pump designed for in-air operation in low-level applications.
• Ensure the pump isn’t running beyond its service factor—if amp readings show overloading, adjust operation by throttling the pump or using a smaller impeller trim.
• Regularly check intake screens for blockages that might starve the pump of fluid.

3. Seal Failure (Water Intrusion)

Cause: Mechanical seals and cable entry seals protect the motor from water intrusion, but they can wear out or get damaged. If a seal fails, water leaks into the motor housing, potentially shorting the motor or causing bearing failure. Abrasive fluids, overheating, and misalignment during installation can accelerate seal wear.

Fix: If water is detected in the motor housing or oil chamber (evident from a moisture sensor alert or milky seal oil), service the pump immediately. This typically involves replacing the mechanical seal and checking the motor insulation for damage.

Prevention:

• Follow the manufacturer’s maintenance schedule for seal replacement, inspecting or replacing seals annually or biannually in heavy-duty applications.
• Prevent dry running, as even brief operation without fluid can overheat and ruin seals.
• Use pumps with hardened seal faces or flush water systems for abrasive fluids.
• Check for early signs of leakage, such as oil or water at weep holes, to catch seal failures before they escalate.

4. Electrical Issues (Power Supply Problems)

Cause: Many pump failures stem from electrical faults such as phase imbalance, low or high voltage, phase loss, or transient surges. A common issue with three-phase pumps is an uneven power supply, where one phase has lower voltage, forcing the motor to draw excess current on another phase, leading to overheating.

Fix: If a pump trips breakers or has high amp draw on one phase, measure voltage on all phases while the pump is off and while it is running. Address any supply issues (e.g., faulty utility feed, improper VFD settings).

Prevention:

• Install phase monitors or overload relays in the control panel to shut off the pump in case of out-of-range voltage or phase loss.
• Keep electrical connections dry and secure to prevent short circuits.
• Use the correct cable gauge and length to prevent undervoltage issues.
• Perform regular megohm (insulation resistance) testing to detect early motor degradation.

5. Improper Installation or Operation

Cause: Installation errors can significantly impact pump performance and lifespan. Common mistakes include:

• Mispositioned or stuck float switches that fail to shut off the pump, causing dry running.
• A missing or faulty check valve, leading to water hammer or backflow, which can damage the impeller and shaft.
• Physical misalignment, such as failing to properly seat a pump on its guide rail, causing vibration and wear.

Fix: Inspect the installation thoroughly if a failure occurs.

• Fix or replace jammed float switches and ensure floats move freely.
• Check and repair the check valve if backflow is slamming the pump.
• Re-seat or realign the pump using proper mounting systems to prevent blow-by or misalignment.

Prevention:

• Always follow the installation guidelines in the pump manual, ensuring proper leveling and secure piping.
• Verify that control switches and valves function correctly before leaving the pump unattended.
• Consider pump protection circuits to detect conditions like dry run or excessive starts.
• Use soft starters or VFDs with pump logic to ramp down speed and prevent water hammer.

Looking for Advice on Submersible Pump Technology?

Most submersible pump failures can be prevented with proactive maintenance and proper installation. Regular inspections help catch a clogged impeller or a weeping seal before these minor issues escalate into full-blown failures. Understanding these common failure modes allows engineers and maintenance teams to implement safeguards—such as better screening, float switches set at safe levels, or electrical protection devices—that can significantly extend a pump’s service life. A well-maintained pump not only lasts longer but also operates more efficiently, delivering better value over time.

HOMA is one of the industry’s best-established submersible pump manufacturers, and we are keen to help you realize maximum efficiency in your facility. Consult our guide on how to choose the right submersible pump, or contact us for further information.

May 9, 2025