After disassembling the machine, it's easy to find the thermostats. They are attached to the top of the boiler with clips. There are two thermostats:

95 ° C - brewing temperature (just below the boiling point of water)

127 ° C - steaming temperature (just below the boiling point of water)

You can test the thermostats with a multimeter set to the resistance (ohms) setting. These thermostats are "normally-closed" which means at room temperature, the thermostat switch is closed. The meter should show close to 0 ohms when connected to the thermostat terminals.

You can remove the thermostats and check to see that they open when their temperature setting is reached. Carefully use a heatgun and an infrared thermometer to heat the thermostat above their set point. If you overheat them, you will melt the plastic case and destroy them. (Not that I did anything like that.... :-) )