Apparatus for treating laundry and control method therefor

A method for controlling a laundry treatment device including a drum configured to receive laundry therein, a duct configured to circulate air discharged from the drum into the drum, a heat exchanger disposed in the duct and configured to dehumidify air in the duct and to heat the dehumidified air, a water collector configured to receive water separated from the air passing through the heat exchanger, a sprayer configured to spray the water to the heat exchanger to remove a foreign substance from the heat exchanger, a pump housing that is connected to the water collector and defines a first pump outlet and a second pump outlet, an impeller configured to move water in the pump housing to the first pump outlet, a drainage housing connected to the water collector, a housing connecting pipe that connects the second pump outlet to the drainage housing, a drain pipe configured to discharge water in the drainage housing, and a drain valve configured to control opening and closing of the drain pipe, a switch housing connected to the first pump outlet, a first supply pipe that connects the switch housing to the sprayer, a second supply pipe that connects the switch housing to the drain pipe, and a switch valve configured to control opening and closing of each of the first supply pipe and the second supply pipe, the method comprising:

• controlling the switch valve to close the first supply pipe and open the second supply pipe;
• controlling the drain valve to open the drain pipe;
• and
• discharging, by rotation of the impeller, the water in the pump housing to the second supply pipe and the housing connecting pipe.