Set thermostat and furnace switches   Do a quick run-through of your system: switch your thermostat to “heat,” set it above your current home temperature, and check that your furnace switch is on for a full system test.

Clean air filters and vents   Clear out clogged vents and registers that block off furnace air flow—and replace your filters regularly to keep your system running smoothly and efficiently.

Turn your pilot light on   Furnace still won’t ignite? It may be your pilot light or ignition sensor. Locate the instructions that came with your furnace to reginite it—or call a pro.