Why does a sump pump fail?
Power Failure: In most cases, a sump pump fails because of a loss of power. There are several reasons you could lose power. There could be a storm causing a local power outage, a tripped circuit breaker or a blown fuse; a damaged power feed line or even something as simple as an unplugged pump. In some cases a wearing sump pump will cause the electrical breaker to trip.
Mechanical Failure: Another common reason for sump pump failure is a mechanical problem, such as a faulty part or an aging pump. The pump may be burned out or jammed with mud or a stone. It could have a broken impeller, drive shaft or the float switch could be stuck or broken. A back up pump isn't going to protect you from mechanical failure so it is wise to purchase a separate alarm that will alert you to a system failure in addition to your backup pump. Most mechanical problems with the sump pump are float related. If the pump does not start, the float may be hanging on something in the tank. A simple repositioning of the pump should solve the problem. If this fails, the float may need replacement. If the pump fails to shut off when the water level drops to the bottom of the sump tank, this indicates you need a new float.
Pump Overload: Pump overload usually occurs when an excess of water flows into the sump pump. When this happens the pump is unable to handle all of the incoming water and it malfunctions. Also, a pump will overload if foreign matter becomes trapped, partially clogging the pump. This will cause the motor to start to run slower and eventually the sump pump will stop working.