Thermal fuse is a heat-sensitive safety feature that shuts down system when overheating is detected.
In electrical wiring, the thermal fuse reacts to high temperature caused by too many amps on the electric circuit. When temperature exceeds the fuse amp rating, then the fuse trips and cuts power to electric circuit.
Example of thermal fuse is a household circuit breaker.
Gas water heaters have a different type of thermal fuse located in the combustion chamber or on the combustion chamber door, and also inside a copper probe inside water tank. Water heater thermal fuses will trip when water temperature exceeds fuse rating, or when heat inside the combustion chamber exceeds temperature rating of fuse. This action will cut off gas supply to water heater.
So a thermal fuse is a safety feature.
Thermostat is not a safety feature.
Thermostat is a measuring tool.
Thermostats measure temperature.
Example of thermostat is outdoor thermometer, or cooking thermometer, or Heat-AC control located on wall inside house.
Thermostats can give a simple temperature reading, or they can cause a separate control to turn on-off depending on application.
For example thermostat on Heat-AC will read room temperature, and when temperature exceeds setting, this triggers a switch that turns Heat-AC on-off.
Many appliances have both thermal safety fuse and thermostat.
Take for example a gas water heater. A copper tube extends into the water tank. Inside the copper tube are 2 things: A thermostat probe to measure water temperature, and a thermal fuse called an ECO for energy cut off. The ECO is a thermal fuse, and is a safety feature.http://waterheatertimer.org/images/Gas-valve-ECO2-358.jpg
The thermostat reads temperature of water, and turns water heater on-off to keep water hot. A person can adjust water temperature by adjusting the thermostat dial on front of water heater.
However if the thermostat fails, or some other problem occurs, and water inside the tank gets hotter than 180 degrees, then the ECO or thermal fuse will trip. When the thermal fuse trips, this turns off gas to the water heater so water cannot get any hotter. The safety device prevents water heater explosion. The water heater must be repaired since this particular thermal fuse cannot be re-used afterwards, and must be replaced.