Most common faults of submersible pumps and how to solve them
Why a submersible pump fails from time to time – and why it’s not always a reason to panic
A submersible pump is one of those devices that earn customer trust precisely because it runs for months or even years without any intervention – submerged in a well or borehole, out of sight, until one day "there is no water". Over the years we have been involved in the sale and servicing of pumping equipment, we have repeatedly confirmed one rule: most faults are not random or unpredictable. They have a cause that could either have been detected in advance or avoided by proper selection and installation. In this article, we will go through the most common submersible pump faults we encounter during warranty claims and service interventions, explain their technical nature, and above all – show you how to prevent them or how to diagnose them before you unnecessarily replace the entire pump.
If you are considering the purchase of a new pump, we recommend first reading the articles How to choose a pump for a well: key selection criteria and What diameter of borehole do you need: the difference between 2", 3" and 4" pumps – this text is more focused on the operation and faults of an already installed pump, or on what to look out for when purchasing to avoid these problems.
How a submersible pump works – the basis for understanding faults
In order to correctly diagnose a fault, it is good to understand at least the basics of what is happening inside the pump. A submersible pump consists of several main components: an electric motor (sealed and insulated, cooled by the surrounding water), a hydraulic part (impellers in centrifugal pumps, or a screw/stator in screw pumps), a check valve, a power cable, and in many cases also a capacitor (in single-phase motors) or control electronics.
It is crucial to understand that the motor is structurally designed to be submerged in water – the water cools it and also lubricates some parts. If the pump runs dry or with insufficient flow around the motor, overheating occurs, which is responsible for a large part of the faults we encounter in practice.
1. The pump is running, but it is not delivering water (or only a minimal amount)
This is one of the most common complaints we deal with. The customer can hear that the motor is running (either directly at the well or through the noise in the pipes in the house), but no water is coming out of the tap, or only a weak trickle. There are several possible causes, and they need to be checked one by one:
Drop in water level below the pump
The most common cause, especially in summer months or during prolonged drought. If the groundwater level drops below the pump’s suction part, the pump is drawing air instead of water and loses its ability to pump – this phenomenon is called loss of suction or "air lock". The solution is either to lower the pump (if the depth of the borehole allows it), or to install a float switch that automatically turns off the pump when the water level drops and protects it from running dry.
Clogged suction filter or clogged impeller
Sand, silt and sediments are a common reality in wells, especially in dug wells or older boreholes without quality casing. If the pump is not protected by a filter, particles get directly into the hydraulics and gradually clog the impeller channels. The flow then decreases gradually, not suddenly – the customer often notices that "the water has been weaker for a while" before it stops completely. In such cases, we strongly recommend installing a 1" sand separator filter for suction, which captures mechanical impurities before they enter the pump and significantly extends its lifespan.
Defective or jammed check valve
The check valve prevents water from flowing back from the pipe into the well after the pump is turned off. If it becomes clogged with impurities or is mechanically damaged, it can either become completely clogged (the pump does not push water at all), or it leaks (water flows back after each shutdown, and the pump has to refill the entire pipe each time it starts, which is manifested as "jerky" water delivery and frequent switching on and off).
Worn screw or impeller
In screw pumps (for example, Submersible screw pump for narrow boreholes STING 2"), natural wear of the rubber stator through which the metal screw passes occurs over time. In sandy water, this wear is faster and is manifested by a gradual decrease in performance – the pump still runs, but the head and flow rate drop. This is a common occurrence in intensively used pumps after 3-5 years of operation in more demanding conditions and is solved by replacing the stator, or the entire pump, if it is more economical.
2. The pump does not start at all
The second most common category of faults – the motor is silent, nothing happens. Diagnosis here is a bit different, as it is more about the electrical part than the hydraulics.
| Symptom | Likely cause | Solution |
|---|---|---|
| Complete silence, no sound or vibration | Power outage, blown fuse, tripped circuit breaker | Check the distribution board, circuit breaker, connection |
| Quiet buzzing, motor does not start | Defective capacitor in a single-phase motor | Replace the capacitor (a common and inexpensive service intervention) |
| Pressure switch clicks, motor does not start | Pressure switch failure or damaged cable | Check the switch, inspect the wiring |
| Motor starts and immediately shuts off (thermal protection) | Overheating, jammed hydraulics, low voltage | Check the voltage, free the rotor, check the cooling |
Damaged power cable
The cable of a submersible pump is constantly stressed by contact with water and possibly mechanically during deployment and retrieval of the pump from the borehole. Micro-cracks in the insulation cause moisture ingress and short circuits or leakage current to ground (earth). This is one of the faults that can be reliably detected by measuring the insulation resistance between the conductors and the cable sheath – the value should be in the range of units to tens of megaohms. If you measure values close to zero, the cable is damaged and must be replaced or the pump must be pulled out and the connection repaired.
Improperly or underdimensioned cable
When drilling deeper wells (over 30-40 m), a common mistake in DIY installation is the use of too thin a supply cable. Voltage drop on a long line will cause the motor at the end to lack the voltage needed to start, especially during startup when the current draw is highest. The motor will either not start at all or will start slowly and overheat. The recommended cable cross-section should always be calculated according to the length of the line and the power of the pump – in case of doubts, it is better to consult with the seller when choosing a specific model.
3. The pump frequently turns on and off (so-called "cycling")
Frequent switching of the pump on and off in short intervals (e.g., every 10-30 seconds) is a phenomenon that significantly shortens the lifespan of the motor and switching components. An electric motor is most stressed precisely during startup, when it draws several times higher current than during steady operation.
Too small or damaged membrane in the pressure tank
Most home water systems operate with a pressure tank (hydrofor), which functions as a reservoir of pressure energy. If the rubber membrane in the tank is cracked or the tank is insufficiently inflated with an air bladder, the usable water volume in the tank drops drastically and the pump must replenish the pressure much more frequently. The solution is simple and inexpensive: check and, if necessary, inflate the air bladder pressure to a value 0.2-0.3 bar lower than the pump's switching pressure (typically set around 1.5 bar with a switching pressure of 1.8-2 bar).
Leaks in the water distribution system
If the system is micro-leaking somewhere (cracked pipe, leaking valve, dripping tap), the pressure in the system slowly drops even without water consumption, causing the pump to start "on its own" without an obvious reason. We recommend always checking this scenario first, as the repair is often just a few dozen euros, while replacing the pump costs hundreds of euros.
4. The pump vibrates, is noisy or makes unusual sounds
Sound is surprisingly an important indicator in diagnosing submersible pumps, even though the pump is located deep underground and we cannot see it directly.
Cavitation
If the pump is operating at the edge of its suction capacity or is improperly dimensioned for a given depth, microscopic vapor bubbles form in the water, which upon collapse cause a characteristic "crackling" sound resembling sand flowing through a pipe. Cavitation causes long-term damage to impellers and the shaft through mechanical erosion. The solution is to properly dimension the pump according to the actual depth of the water level – this topic is discussed in detail in the article What power and head to choose for a pump according to well depth.
Worn bearings
In centrifugal pumps such as Submersible pump IBO 3" STM 20, bearings can wear out after many years of operation. This is indicated by a buzzing or squeaking sound and increased vibrations, which can even be felt on the discharge pipe at the well head. This usually signals the end of the pump's life expectancy and replacement should be expected within months.
Foreign object in the hydraulics
Sometimes a larger piece of dirt (a stone, a piece of flaking casing) gets into the pump, causing an irregular, knocking sound and increased current draw. In the worst case, the rotor may become completely blocked. Prevention is again the best approach – installation of a suction filter before the pump significantly reduces the risk of this scenario.
5. The pump overheats and the thermal fuse trips
Modern pumps have built-in thermal protection that automatically turns off the motor when it overheats. If this happens repeatedly, it is a symptom, not the fault itself – the cause of overheating must be found.
- Insufficient cooling – the pump is placed too high, above the level of sufficient water flow around the motor, or the well is too narrow and does not allow circulation of water around the motor housing.
- Dry running – repeated short-term operation of the pump without sufficient water supply, typically in wells with low yield during summer months.
- Hydraulic overload – the pump is operating outside its performance characteristics, for example at a head significantly higher than the rated parameters.
- Fluctuating voltage in the grid – especially in rural areas with weaker electrical connections, where voltage drop during startup causes higher current draw and thus higher heating of the windings.
In practice, we recommend disconnecting the pump from the power supply for 15-20 minutes in case of repeated thermal shutdowns, letting it cool down, and then measuring the current draw during restart using a clamp meter. If the current significantly exceeds the rated value stated on the pump's nameplate, the problem is in the hydraulic part or the power supply, not in the thermal fuse itself.
6. Sand and mechanical impurities in the water
This issue does not directly affect the functionality of the pump, but the quality of the supplied water – paradoxically, it is one of the most common reasons why pumps fail prematurely. Sand in the water acts as an abrasive material, gradually damaging seals, impellers, and the shaft bearing.
The solution to this problem always has two levels. The first is short-term – installation of a mechanical sand separator filter 1" on suction directly on the pump discharge, which captures particles before they enter the household water system and cause problems in taps, valves, or the washing machine. The second is long-term – checking the condition of the casing and filtering the well, since a constant supply of sand indicates either a damaged casing pipe perforation or an improperly constructed well backfill. In such cases, it is advisable to contact a well driller, as the filter only addresses the symptom, not the cause.
7. Differences in failure rates between rotary and centrifugal pumps
When troubleshooting, it is useful to know that rotary and centrifugal pumps have different "weak points", since they operate on different principles. A detailed comparison can be found in the article Submersible rotary vs. centrifugal pump – differences and applications, here we summarize only the service perspective.
| Type of pump | Typical failures | Sensitivity to sand |
|---|---|---|
| Rotary (e.g. STING 2") | Wear of rubber stator, gradual performance drop | Moderate – rubber is more durable, but wear is gradual |
| Centrifugal (e.g. IBO 3" STM 20) | Wear of impellers, bearings, sudden performance drop | High – metal/plastic impellers are quickly abraded by sand |
Rotary pumps for narrow bores (2") generally handle slightly contaminated water better, but have a lower maximum flow rate. Centrifugal pumps for wider bores (3" and more) have higher performance and flow rate, but are more sensitive to abrasive particles. When choosing between specific models, we also recommend reading the article Comparison of STING and IBO pumps – which one to choose, where we address the topic from the perspective of performance and application.
8. Installation errors that later appear as "pump failure"
Surprisingly, a large portion of complaints that initially appear to be a manufacturing defect in the pump actually originate from incorrect installation. In practice, we most commonly see these errors:
Pump suspended too low, in silt at the bottom of the bore
Sediments at the bottom of the well are stirred up during pump operation and are directly drawn into the hydraulic system. The correct recommendation is to suspend the pump at least 1-1.5 m above the bottom of the bore (provided the water column height allows it) and ideally to position the suction part even higher, taking into account water level fluctuations.
Missing or undersized protection
The absence of a residual current device or a motor circuit breaker with the exact value according to the pump's rated current causes the pump not to shut off in time during minor faults (e.g., partial jamming), leading to further damage and eventually total motor failure.
Poor pump attachment and suspension
A pump suspended only on the discharge pipe without a safety rope can fall to the bottom of the bore if the threaded connection is damaged. We always recommend using stainless steel or high-quality polypropylene safety ropes that carry the weight of the pump independently of the piping. A detailed description of the correct installation procedure can be found in the article Installation of a submersible pump in a well or narrow bore.
9. When is repair worth it and when is it better to replace the whole pump
This question troubles most customers who are dealing with a pump failure in a unit older than 5-7 years. Our practical experience is as follows:
- Repair is worth it if it involves replacing a capacitor, check valve, gasket, or in the case of rotary pumps, the stator – these parts are relatively inexpensive and the work is quick.
- Replacement of the entire pump is worth it if the motor winding is damaged (burnout, inter-turn short), the pump is older than 8-10 years and has already been repaired once, or if the cost of spare parts exceeds 50-60% of the price of a new pump.
- Energy efficiency should also be considered – older pumps have lower efficiency than modern models, so higher electricity consumption can make the investment in a new pump pay off through lower operating costs.
10. Preventive maintenance that prevents most failures
From the service interventions we handle, it is clearly visible that at least 60-70% of failures could be prevented with simple preventive care. We recommend:
- Check the air pressure in the pressure tank's air bladder once a year.
- Monitor the operating sounds of the pump and notice any changes compared to the normal condition.
- For wells with higher sand content, install a sand filter during installation, not after the first failure.
- Check the condition of the power cable each time the pump is removed (e.g., during well cleaning).
- Do not overload the pump by operating it outside its working point – if the water level drops significantly, it is better to address the pump relocation or install a float switch, rather than let the pump run at the edge of suction repeatedly.
- When selecting a new pump, carefully consider the parameters according to the actual depth and yield of the well – incorrectly oversized or undersized pumps are more prone to failures in the long run.
Frequently asked questions (FAQ)
The pump is running, but no water is flowing at all. What should I check first?
First, check the water level in the bore – if it has dropped below the pump level, it is a loss of suction. If the water level is fine, check the check valve and suction filter, which may be clogged with dirt. Only then is it reasonable to consider mechanical damage to the hydraulics.
How can I tell that there is too much sand in my well for a standard pump?
Typical signs include cloudy water after starting the pump, a grinding sound resembling sand being poured, and a gradual drop in pump performance over months. In such a case, we recommend installing a sand filter and considering a check of the well casing and screen.
Why does my pump frequently turn on and off even without water being drawn?
The most common cause is a cracked membrane in the pressure tank or insufficient air pressure in the air bladder. Another possibility is a leak somewhere in the system – check all connections, valves, and taps for leaks.
Is it normal for the pump to get warm during operation?
Mild heating is normal, as the motor is an electrical device under load. A problem arises if the pump overheats to the point that the thermal protection repeatedly trips – this is always a sign that something is wrong with cooling, water level, or hydraulics.
Can a progressive cavity pump be repaired, or must the entire unit always be replaced?
In most cases, only the worn rubber stator can be replaced on progressive cavity pumps, which is a significantly more cost-effective solution than purchasing a new pump. The rotor itself (the metal part) has a much longer service life and usually does not need to be replaced at the same time as the stator.
How long should a submersible pump in a well last without failure?
With proper installation, appropriate water quality, and preventive protection against sand, the typical service life of a quality submersible pump ranges from 8 to 15 years. In demanding conditions (high sand content, frequent water level fluctuations, weak electrical grid), this period can be significantly shortened unless suitable preventive measures are taken.
Conclusion
Most faults in submersible pumps have a clear and logical cause that can be identified without unnecessarily pulling the entire pump out of the well, especially with some experience and a systematic approach. The key is to start with the simplest and most cost-effective checks (power supply, water level, pressure tank) and move toward more complex interventions (insulation testing, disassembly and hydraulic inspection). At the same time, it is true that investing in the correct pump selection, quality installation, and basic prevention—such as a sand filter or safety rope—always pays off in the form of fewer faults and a longer system lifespan. If you are unsure about diagnosing a specific issue or are considering replacing your pump with a new one, you can find the full range in the category Pumps for wells, where you can also compare specific models according to the well diameter and required performance.
Do you have a question about this topic?
Having trouble deciding or dealing with a specific situation in your home? Write to us—we are happy to help.