Start with the thermostat: if the fan is set to ON instead of AUTO, it blows air even when the furnace isn’t heating. Then check the filter. A clogged filter can overheat the furnace and trip a safety switch that shuts the burners off while the blower keeps running.

If those are fine, the usual causes are a dirty flame sensor that shuts the burner off seconds after it lights, a failed igniter, a gas supply problem, or a blocked condensate drain on a high-efficiency furnace. In snow country, check the white plastic intake and exhaust pipes outside: drifting snow or ice can block them and shut the furnace down. Clear them gently if you can reach them safely.

Furnace repair is offered by our St. George & Hurricane team, which also offers 24/7 emergency HVAC. Our Flagstaff, Durango and Jackson teams don’t repair furnaces; our Durango team services boilers and radiant heat instead.