If your furnace makes odd noises, you should hire a professional as soon as possible. There are a few other indicators that your furnace needs professional attention. Excessive soot could mean your burners need adjustment or that the heat exchanger needs replacing. If your flame is pale in color or irregular, this can indicate dirty burners or a cracked heat exchanger. This is a potential hazard and requires a professional to investigate. If your furnace is short-cycling (which means it only runs for a short period of time before shutting off), you may have a thermostat issue or an overheating exchanger. This also requires the expertise of a professional.