A furnace that won't fire up is one of the most common winter emergencies. Before anything else, check that the thermostat is set to heat and above room temperature, confirm the breaker hasn't tripped, replace a dirty filter, make sure the furnace power switch is on, verify the gas valve is open, check that the pilot or igniter is working, and confirm the condensate drain isn't full and triggering a safety shutoff. If heat still won't come on, it's time for a pro — a no-heat call in winter shouldn't wait.
This article is general guidance, not a substitute for a licensed technician. When in doubt, call (866) 803-4910 and we'll connect you with a local pro 24/7.