Heaters are the most important equipment in an aquarium. Lights can fail, filters can fail, and both will be seen and dealt with. But a malfunctioning heater can cook a tank of fish overnight, or the opposite. So always buy the best heater, even if it costs more. Inexpensive brands are more likely to fail.
Second, was this heater functioning correctly for a time before this happened? Hypothetical question really, as there is nothing we can do now, but I ask it because the temperature setting on many even good brand heaters is not always exact; I have heaters set at 70F/21C that maintain the tank at 76F/24C. But the heater is not malfunctioning, it keeps the tank constant. It just took a bit of trial to get the setting where it needs to be for this heater.
Third point, the lower wattage heaters tend to give oput more than higher wattage. I have had 50w heaters fail, to the extent that I won't even buy them any longer. But my 100w, 150w and 200w heaters have functioned perfectly, some of them since the late 1990's.
My latest heater purchase for a new tank was Eheim Jager, a brand I trust. I have three Fluvals, and two seem fine but one acted up so I took it out to avoid risks.
Byron.