The answer to 'why is my heat exchanger not working' is that the heat exchanger, which is a critical component of your furnace, may not be functioning properly. This can be caused by a variety of issues, including cracks, corrosion, or a buildup of soot and debris.
Some common symptoms of a failing heat exchanger include strange noises coming from the furnace, reduced heat output, and a pilot light that keeps going out. In some cases, a malfunctioning heat exchanger can even be a safety hazard, as it may allow dangerous carbon monoxide to leak into your home. If you suspect an issue with your heat exchanger, it's important to have a professional HVAC technician inspect and diagnose the problem as soon as possible.