Thank you for your question. Without having the model number of our dryer I will only be able to provide general information. Generally speaking, the thermal fuse will fail when there is a venting restriction/blockage or if the dryer is getting to hot. If it's an electric dryer then it could have a shorted heating element causing the heater to stay on or it could have a faulty operating thermostat if it's gas or electric.
Reply with the model number for model specific information.