The answer to 'heat exchanger not heating' is that a faulty or damaged heat exchanger is the most common cause. This can happen due to cracks, corrosion, or other wear and tear over time. Symptoms include uneven heating, strange noises, or even a gas leak. The solution typically requires replacing the heat exchanger, which is a major repair best handled by a professional HVAC technician.
Trying to repair or replace the heat exchanger yourself is generally not recommended, as it can be dangerous if not done properly. Heat exchangers contain hazardous gases and require specialized tools and expertise to service safely. Attempting DIY repairs could potentially lead to gas leaks, fires, or other serious issues. It's always best to call in a certified HVAC professional to diagnose and fix a problem with your heat exchanger.