Doesn't come on. Check whether thermostat is set below room temperature. Check whether pilot light is out. If pilot is out, first shut off the A valve, which is the main gas valve to the burner, and the B pilot valve. Wait five minutes. Then turn on B valve and ignite with a match. (In some burners there is a magnetic valve directly in front of the burner, and B valve is attached to or built into a solenoid valve. A red button represents the B valve. Depress this and then put match to pilot tip. Keep the red button depressed for 1 minute to energize the magnetic valve.) Finally, turn on the A valve. If burner still doesn't go on, call a serviceman.
Note. Instructions for lighting pilot lights are mounted on the burner. Don't let these get obliterated with dirt and grease.
Pilot lights, but burner doesn't work. Check whether electric fuse controlling burner circuit has blown.
Smells. Shut off main gas control valve at once and call a serviceman. Don't under any circumstances go hunting for the leak with a lighted match. Don't even turn on the electric light in the furnace room.