Natural gas furnaces require several safety components to help protect your family, your home, and the furnace itself. These sensors help to detect unsafe conditions and shut the unit down before more severe damage can occur. Overheating is one reason for a furnace to trigger a safety shut down, and it's a problem that usually results from a few common underlying issues.
If your furnace runs for a short amount of time and immediately shuts down or shuts down and refuses to turn back on, there's a good chance it may be overheating. Your furnace may also display an error code or turn on a visible warning light on its control board. While overheating can occur for many reasons, there's a good chance that one of these three failures is the culprit.
1. Airflow Restrictions
Airflow restrictions cause your furnace to overheat since hot air remains too close to the heat exchanger for too long. Without fresh air blowing across the exchanger surface, it can reach unsafe temperatures. An overheated exchanger will eventually crack, allowing potentially dangerous combustion gases to leak into your home. Modern furnaces shut down to prevent this situation.
Airflow restrictions may have numerous causes, but the filter is one you can check yourself. Always replace filters before they become too visibly dirty or clogged up. You should also check for restrictions near return vents, such as furniture or boxes that may be preventing airflow from reaching the filter in the first place.
2. Dirty Heat Exchanger
Dust and debris typically shouldn't find their way to your heat exchanger, but this can occur if your filter is too dirty or you try to run the system without a filter. Your heat exchanger is essentially a coil that transfers heat between the furnace combustion gases and the ambient air. Dust can act as an insulator, preventing the exchanger from transferring heat.
An excellent way to avoid this situation is by scheduling an annual HVAC service. Technicians will usually inspect and clean your heat exchanger as part of this job, ensuring that dust doesn't build up to sufficient levels to impact your furnace's operation.
3. Bad Blower
Airflow restrictions are harmful, but no airflow at all is a much more dire situation. If your blower motor fails, air won't move across your heat exchanger at all. In these cases, your furnace will usually shut down relatively quickly, and you won't notice any airflow at all from your vents. Attempting to force your furnace to run with a bad blower motor can cause severe damage to the heat exchanger.
Remember that overheating is a serious situation. If your furnace's safety equipment shuts the unit down, it's doing so for a good reason. When you suspect your furnace may be overheating, contact local residential heating services to diagnose and repair the problem safely.