Visible rust or stains on vents and chimneys. Loose masonry on chimney. Loose or missing furnace panel. An appliance that makes unusual sounds or emits an unusual smell. An appliance that keeps shutting off.
Many appliances have safety devices installed that prevent dangerous operation of the unit.
An appliance which constantly shuts off may be an indication that the appliance is not safe. Call a service repairman to test the appliance before you try to operate the unit again. If you suspect that you are experiencing poisoning, get fresh air immediately. Open windows and doors for more ventilation, turn off combustion appliances and leave the house. Be alert to symptoms of CO poisoning.