The answer to 'heat exchanger not turning on' is that a malfunctioning heat exchanger is a serious issue that requires professional diagnosis and repair. The heat exchanger is a critical component of your furnace or HVAC system that transfers heat from the combustion process to the air that circulates through your home. If the heat exchanger is not turning on, it could be due to a variety of problems, including a faulty thermostat, issues with the blower motor, or a crack or leak in the heat exchanger itself.
If your heat exchanger is not functioning, it's important to have a qualified HVAC technician inspect the system as soon as possible. Continuing to operate a furnace with a malfunctioning heat exchanger can be dangerous, as it may lead to the release of carbon monoxide or other harmful byproducts. A professional will be able to diagnose the root cause of the problem and recommend the appropriate repairs or replacement.