There is only one fuse and that's the thermal fuse on the blower housing. It is in the motor circuit, not the heat circuit. The device at top of heater box is a thermal cutoff and the device at bottom of heater box is the hi limit thermostat. So yes, it now sounds like the thermal fuse has blown. The hi limit and thermal cutoff don't regulate the heat, they are only safety devices. If it gets too hot in the heater box, the hi limit should start cycling the heat coil and if that fails, the thermal cutoff will trip and kill power to the heat coil permanently. The operating thermostat on the blower housing is what regulates the heat. So, I'd say you either have a faulty operating thermostat or an air flow problem. Air flow problem can be caused by excess lint buildup in the internal/external duct, faulty seals at drum or blower housing causing leaks or the blower wheel slipping on motor shaft. If the air flow at exhaust on back of dryer seems sufficient, then looks like the operating thermostat is not opening at the proper temperature or is stuck closed and not opening at all. It can be checked on a hot plate.