Sump pumps can break in the "on" position for a variety of reasons, but one of the most common reasons that a sump pump would turn on and then stay on is because of a part of the sump pump called the float switch. The float switch controls when the sump pump turns on and off. If the float switch breaks, the sump pump could remain on even when there's no water to be pumped. If the sump pump stays on, this could cause the motor on the pump to burn out pretty quickly.
Can the float switch be fixed?
Fixing the float switch on the sump pump would likely require the help of a professional (unless you're very mechanically inclined). However, there is another solution--one that can easily be handled by many DIYers. To fix the problem, you can buy a mechanical float.
What is a mechanical float?
A mechanical float is a switch that comes separate from the sump pump. It has a piggyback power cord that gets plugged in first, and the sump pump is plugged into the switch. The switch then controls the power to the sump. To install the mechanical float, you'll buoy it to something in the sump pump pit, usually the sump pump itself. When the water in the pit rises, the float rises up and the switch is activated. When the water level drops, the float drops with it and shuts off the pump.
How can you install a mechanical float?
Cut the power to the outlet that controls the sump pump, then unplug the sump pump. Plug in the mechanical float, then plug the sump pump into the piggyback part of the mechanical float's power cord. Put the mechanical float into the sump pump pit. The mechanical float will likely have a metal bracket you can use to tether the float to the sump pump, but a plastic zip tie will have the same effect and will be easier to use.
Tether the float to the pump, giving it a few inches of slack so the float can rise and fall with the water levels in the pit. Then, turn the power back on to the sump pump. Fill the pit with water and see if the float works. If the float doesn't work, then it's time to contact a plumbing professional like AA Plumbing. He or she can help you fix your problem.