How do you reset a furnace high-limit switch?

To troubleshoot and reset a furnace limit switch, ensure the furnace is receiving power, turn off the furnace switch, replace the filter and test and replace the high-limit switch. Consult a professional with questions or to perform any necessary repairs.

The high-limit switch on a furnace turns the furnace off when it starts to overheat and signals for the blower fan to turn on and cool down the heat exchanger. After the system cools, the furnace will turn back on. If a problem exists and the furnace turns off four or five times, the furnace will not turn back on until the problem is addressed. To troubleshoot issues with the high-limit switch.

1. Check for power

Check the breakers and ensure that power is going to the furnace.

2. Reset the furnace switch

Turn off the switch by the furnace and keep it off for 5 minutes. Then turn it back on to see if that resets the furnace.

3. Replace the filter

A dirty filter will overheat the furnace. Replace or clean the filter and turn the furnace back on.

4. Test the high-limit switch

Use a continuity tester on the switch terminals on the high-limit switch to ensure it is working properly. If the light on the tester does not turn on, the switch needs to be replaced.

5. Replace the high-limit switch

If the switch is bad, remove the screws and pull it out, noting the position of the sensor. Install the new high-limit switch with the sensor in the same position.