Charles C. Roberts, Ph.D., P.E.


Sump pump failures lead to substantial water losses and insurance claims that require the attention of claims representatives. There are a variety of failure modes associated with sump pumps, some covered by insurance, others not. Before proceeding to discussing typical failure modes, a brief review of sump pump system technology may be helpful.

Figure 1A

Figure 1A depicts a typical submersible sump pump system where the pump motor is in a waterproof enclosure and designed to operate below water level. A float switch is used to control operation and comes in a variety of designs, including the free floating type (Figure 1A) as well as internal float or diaphragm designs. A check valve is typically installed to reduce excessive cycling of the pump from back flow.


Figure 1B

Figure 1B shows a pedestal sump pump where the electric motor must be above the water level, since it is not in a waterproof enclosure. The float switch is at the motor and is usually not waterproof. The discharge piping and check valve are the same as that of the submersible sump pump. The pedestal and submersible sump pumps are the most common.


Sump pumps fail to operate for one or more of the following reasons:


1.     Power failure

2.     Improper installation

3.     Improper or lack of maintenance

4.     Wear out

5.     Defective manufacture


The following is a review of typical failure modes, taken from actual losses involving sump pumps. Power failure is probably the most common cause of sump pump failure. Electrical power outage without a battery or auxiliary generator back up, results in many flooded basements. Occasionally, even back-up systems fail especially during long term outages. Batteries loose capacity over time and may not be able to power a pump for sufficient time during the power outage. Battery chargers may also fail, leaving a dead battery. Certainly, proper maintenance of these systems plays a major role in reducing failure rate. Another form of power outage is branch circuit failure brought on by too many other appliances plugged into the same circuit as

Figure 2

that supplying electricity to the sump pump. Figure 2 shows a sump pump system that failed as a result of branch circuit overloading, considered an improper installation. When a power fluctuation occurs in such an overloaded circuit, the starting current, which is often much higher than the steady state operating current, from the other appliances as well as the sump pump will trip the breaker and render the sump pump system inoperative.   A dedicated circuit for the sump pump is certainly recommended.


Figure 3 is a view of a sump pump plug that was connected to an extension cord. Rust patterns on the plug suggest that the connection was occasionally under water which caused the circuit breaker to trip and sump pump failure, an improper installation. It is not recommended to attach extension cords to sump pumps. Extension cords offer increased electrical resistance, which can drop voltage and damage pump motors. Also the connection (Figure 3) can fall into the sump, an electrical safety hazard as well as a possible obstruction to normal pump operation. 


Figure 3


Figure 4

Interference with mechanical operation of the pump is another common cause of sump pump failure. Sump pits with gravel bottoms are susceptible to this. Figure 4 shows a rock jammed in a sump pump impeller, causing sump pump failure and a water loss. Interference of the float switch also can cause sump pump failure. These are both maintenance related causes of sump pump failure.

Figure 5

Internal failure of sump pumps occur as a result of wear out or manufacturing defect. In Figure 5, a winding failure in the single phase motor caused non operation of a new sump pump, which was attributed to a manufacturing defect. There was premature insulation breakdown on stator windings after a very short usage time, a manufacturing defect in this case. 

Figure 6


Figure 6 is a view of failed contacts on the pump float switch. This particular case is a wear out failure that was brought on by improper installation. Drain back of water, as the result of a lack of a check valve in the system, caused excessive cycling of the switch and premature failure of the switch. Early contact failure can also be a result of a manufacturing defect such as improper plating or excessive current draw by the motor. The expected life of a sump pump is approximately 10 years, but varies depending on operating hours and number of start/stop cycles.


Figure 7


Figure 7 is an example of an improper wiring job on a pedestal sump pump. What is depicted, is the float switch wiring with the arrow pointing to chaffed insulation as a result of interference with the float switch push rod. As the push rod rises to turn on the switch, the push rod retainer clip chafed against the hot wire, which shorted out, tripping the circuit breaker. The pump failed to operate during a vacation period, flooding the finished basement.


Care should be taken in handling pumps involved in basement water losses. Removal of the pump in order to send it out for analysis may dislodge a rock (Figure 4) that caused a malfunction. With the rock dislodged, the pump may operate properly. If the pump must be removed and sent out for analysis, it is recommended that a description of the system, along with photographs, accompany the pump to aid the analyst in determining the probable cause of sump pump failure.