Blower motor won't shut off even with thrmostate down on lowest setting and its already hot in house ?why

Defective fan and limit control.
Defective blower relay
Thermostat turned to blower on instead of automatic.
Shorted thermostat wires.

Now if the burner in the furnace is also still running while the blower is running then the furnace is getting a call for heat and the thermostat or thermostat wires are probably the cause. If this is the case remove the W and R wire from the terminal strip inside the furnace. The will cause the burner to turn off and eventually the blower once all the heat is removed from the heat exchanger in the furnace.