Push down the thermostat valve and insert a string between the valve and the valve seat.
Place the thermostat and a thermometer in a container with water and gradually heat the water [Figure 60-50-16].
Hold the string to suspend the thermostat in the water.
When the water temperature rises, the thermostat valve will open, allowing it to fall down from the string.
Continue heating the water and read the temperature when the valve has risen by about 8 mm (0.315 in.).
If the measurement is not acceptable, replace the thermostat.
