Your gas- or oil-burning furnace must be receiving fuel to work. On a gas-fired furnace, be sure the valve on the gas pipe is turned on (the lug or handle should be in line with the gas pipe). On an oil furnace, check the fuel supply.

Unless your furnace has electronic ignition, be sure the pilot light is lit. Check your owner's manual or the instructions posted inside the furnace cabinet for pilot light information. If necessary, relight the pilot.

Look for a reset switch (see your owner's manual), and push it. If the furnace ignites but fails again, call a furnace repair technician.

On an electronic-ignition furnace, turn down the thermostat or turn the power switch off and then on again to reset the ignition control module.

Listen for the sound of the spark or watch for the hot surface ignitor to glow (see your owner's manual). If the furnace doesn't ignite, call a furnace repair technician.