I would say the friction of the water circulating around the pump caused the heat (in combination to the heat from the motor). The float is stuck and there is simply nothing to pump out. I would not suspect a plugged discharge unless the pit was full. Pumps can only pump out to a certain level, as little as 1/2" depth for some, much more for others. When there isn't enough depth for the pump to prime, it will cavitate. Cavitation and the friction of the water molecules creates heat. If water were coming into the pit, the water would be much cooler, probably around 50-55 degrees.

BTW, I would recommend replacement of the pump as they are not designed to run continuously for long periods of time.

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