The F24 indicates a problem in the water temperature sensor. It can occur due to a poor wiring connection between the control board and the sensor. Also, either unit could have gone faulty.
The sensor (24) is located at the bottom front part of the tub area (see the image below).
To get to the temperature sensor, remove the bottom panel below the door. Unplug it and check the resistance using an ohm meter. Check the indications against those specified in the chart below. If they match, the sensor is ok, and you need to check the wiring between the sensor and the control board. Find the TH2 letters, which denote the temp sensor connection. Disconnect the two wires and test the connection with the ohm meter. The indication should be the same as at the sensor itself. If it is, there is a problem in the control board, so it needs to be repaired or replaced.