All heaters go bad, so a lot of people put them on controllers such as Reef Keeper Lite 120 bucks Apex Jr 150 bucks a ranco controller 50 to 70 bucks, it can get expensive but the controller also can turn your lights on and off and control fans when the tanks gets to hot. This is a good investment and worth saving for.
Cobalt came out with a new heater maybe something to take a chance at, most people use Eheim Ebo jager heaters but they still can fail I have one that will not shut off but Eheim gave me a new one.