Dishwasher and controlling method therefor

A method of controlling a dishwasher that includes a tub defining a washing chamber, a sump configured to store washing water, a steam nozzle configured to supply steam to the washing chamber, a spray nozzle configured to supply washing water to the washing chamber, a washing pump including a housing and an impeller rotatably disposed in an upper chamber of the housing, the washing pump being configured to supply steam to the steam nozzle or to supply washing water to the spray nozzle, a heater disposed in the washing pump and configured to heat washing water in the washing pump, a steam supply pipe connecting the upper chamber to the steam nozzle, a washing water supply pipe connecting the upper chamber to the spray nozzle, and a selector valve disposed at the steam supply pipe and configured to open and close a supply path, the selector valve including (i) a valve body that defines the supply path and has an inlet and an outlet disposed higher than the inlet and (ii) a valve ball disposed inside the valve body, the selector valve being configured to close the supply path based on the valve ball being positioned at the outlet of the valve body, wherein the supply path is configured to be closed based on a rotational speed of the impeller being greater than or equal to a first set rotational speed, the method comprising:

• supplying washing water to the sump;
• rotating the impeller by a washing motor to supply washing water from the sump to the washing pump;
• performing a first steam supplying operation that includes operating the heater and supplying steam generated in the washing pump to the steam nozzle through the supply path;
• and
• performing a second steam supplying operation that includes stopping operation of the heater and supplying steam in the washing pump to the steam nozzle by rotating the impeller at a second set rotational speed less than the first set rotational speed by the washing motor, the supply path being configured to be opened based on the rotational speed of the impeller being less than the first set rotational speed.