An F24 error code indicates a water temperature sensor error. You can check the wiring connections at the temperature sensor. If both wires are connected and are making a good connection then the temperature sensor will need to disconnected and tested with an ohm meter. The temperature sensor changes its resistance with temperature. The sensor should have a resistance measurement of 9.7k ohms at temperature of 86 degrees.
Below I have provided you with an image that will help you diagnose the problem.