Why does the trumpet only work on second valve?

My son has been playing the trombone and recently rented a trumpet to try playing it. He can make a sound when he presses down the second valve, but no sound comes if none of the valves are pressed. Also, valves 1 and 3 make no sound when pressed. Is he not playing it correctly or does something need to be adjusted? The rest of us tried playing it and had the same result.