My Lennox Furnace Doesn't Start

Thermostat

• A Lennox furnace may not start because of an issue with the thermostat. Check the thermostat to ensure that it is set at the proper temperature to activate the furnace. Also, make sure the thermostat is set on “heat.” If the settings are correct, turn the thermostat off and on again to reset it. In addition, depending on your thermostat model, Lennox recommends resetting the thermostat using the reset button. Inside the thermostat’s door, on the right side of the thermostat, under “settings,” is an unlabeled, recessed button. Use a thin object like the end of a paper clip to depress this button. Note, however, that resetting a thermostat will delete all of its settings, so they will have to be reprogrammed.

Power Outage

• Fuse or breaker issues may also prevent the furnace from starting. In homes with fuse boxes, check the fuse for the furnace to see if it has blown. If it has, replace it. If you have a breaker box, check the breaker for the furnace to see if it has been tripped. If so, reset the breaker by turning it completely off and then back on again.

Emergency Shut Off

• If the furnace’s shut-off switch is in the wrong position, the furnace will not start. This switch resembles a regular light switch and should be located in close proximity to the furnace. Although it is an emergency furnace shut-off option, the switch is sometimes accidentally switched off. When this happens, the switch will override the thermostat’s control of the furnace. Switch the flip back on to restore furnace control to the thermostat.

Furnace Door

• The furnace may not start because the furnace door is not in its proper position. As a safety mechanism, the furnace will not start if the furnace door is not completely closed. Completely open and then close the door again, and inspect it to ensure that it is closing securely.