I have a 10 gallon tank that I temporarily moved fish & snails out of. I bought the "Via Aqua quartz heater 100 watt"
I carefully read all instructions. I put the heater in the tank vertically and let it get used to tank temp for 15 minutes before plugging in. I got it ready and set it at 79 degrees. But then I thought about it for a minute and I figured I'd set it down a few degrees because I figured if it heated it a little cooler it'd be easier to heat it more rather than cool it down. So I turned the knob down to 75 and the "on" light shut off. And it will not turn on again.