If your heater is sticking even at all throw it away or take it back and get a different kind!!!! One night my heater stuck on and killed or retarded all of my fish. I lost an 8" bluegill a 13" sicilian worm, 8" Albino Tiger Oscar, a 7" GT, a 11" Red Snakehead. And my RD ended up getting an air bubble in one of his eyes and was never the same, his equilibrium was all messed up and he wouldn't eat. My two firemouths ended up okay but they had to bury themselves in the gravel and basically ripped almost all of their scales off to do so. I was not pleased my temp ended up somewhere in the high 90's but it would not register on my thermometer.