Appalachian Wood Stove (120F Recessed) Thermodisc. Part: 4T120R. This switch closes at 120 degrees. When the switch is heated and closes, it completes the circuit supplying power to the fan, allowing the blower to operate. If your fan is not operating or your fan is staying on for an extended period of time after the unit has cooled, this may indicate that there is an issue with the switch.