When selecting a sump pump for your home, you will have to decide if you want an external or submersible pump. An external sump pump has the motor installed above the surface level, making it much easier to service the pump. That said, they are not without their own set of problems. An external sump pump can stop working for any of these 3 reasons.
Sediment will be brought into the well over time. This can cause the well to form a sludge on the bottom. When enough sludge builds up, it can clog up your sump pump and prevent it from pumping water away from your home.
The solution is not fun as it involves shoveling all that sediment out by hand so that the sump pump does not have anything that can obstruct the pipes underwater. Thankfully, this is not a job you have to do with any regularity.
The sump pump works with a float that is attached to a metal rod. As the water fills up in the well, the float and rod will rise. When the water gets high enough, the rod will activate a float switch that turns on the sump pump, and shuts it off as the float and rod come back down.
This rod can become rusty over time. If the rust is preventing the rod from moving up, it will never activate the float switch. You can fix it by using sand paper to smooth out and rust that is on the rod.
The float needs to have enough pressure behind it to flip the float switch when it reaches the proper level. A float that is damaged will fill up with water, sink under the water surface level in the well, and get stuck at the point where it needs to put the necessary pressure on that float switch.
You will need to replace the float to fix the problem. Make sure that the replacement float has a buoyancy rating that matches your existing float. For example, a plastic float of the same size may not have as high of a buoyancy rating as a float made of copper, even though they are the same size.
For other problems such as a broken float switch or a motor that doesn't work anymore, you will need the help of a professional plumber. They can help track down the parts you need and perform the repair for you. Trenchless Pipe Technologies may be able to meet your needs in this area.