There are mainly two reasons why the float switch fails. The first is the use of extension cords which may lead to overheating in the sump pump. When the power source fluctuates in giving power, the float switch despite working cannot really turn the sump pump on. This in the long run also stops the floats witch from working. Apart from that, a float switch may get clogged. The clog will prevent it from rising up from the base. As a result, it will not do what it is supposed to do.