Is my Top Fin Heater broken?

Okay so i got my third heater yesterday nd i put it in water, let it sit unplugged 30 minutes, and then i plugged it in. One day later my water is 60F. I set it to the middle level and the water was supposed to be 73F. I set it to the highest level and the water is still 60F. Btw the heater is a 50 watt submersible Top Fin heater. I used 2 tetra heaters before but they kept the water MUCH colder.