A furnace problem becomes an emergency when it presents a possible fire, gas, electrical, or carbon monoxide hazard, or when the loss of heat creates an immediate risk to people or the property. A carbon monoxide alarm, natural gas odor, smoke, repeated breaker trips, or complete furnace failure during freezing weather calls for immediate action.
Carbon monoxide is colorless and odorless. If a carbon monoxide alarm sounds, move everyone outside, call emergency services, and remain out of the property until responders say it is safe to return. The furnace should not be operated again until the source has been identified and serviced.