Some Chattanooga and Whitehall hot pack heating units use over‐temperature sensors to safeguard against a thermostat failure. The operational thermostat is set to maintain a temperature between 160°
– 167°F, while the over‐temperature sensor is designed to trip around 190°F. In the event the operational thermostat fails, the heating element will either not turn on or worse, not turn off. The
former results in room temperature water, while the latter results in boiling water leading to evaporation and eventual heating element destruction. The over‐temperature sensor prevents the
water from boiling in the event of an operational thermostat failure. There are times, however, when the over‐temperature sensor itself fails by tripping at a lower temperature. To recognize the water temperature at the time the over‐temperature sensor trips is helpful to pinpoint which of the thermostats is failing.