Furnace Not Kicking On Automatically: Troubleshooting Tips

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As the temperatures drop and winter sets in, it can be quite frustrating to find that your furnace is not kicking on automatically. This can lead to discomfort and even potential health risks if not addressed promptly. In this article, we will explore some common reasons why your furnace may not be starting automatically and provide troubleshooting tips to help you resolve the issue.

1. Check the Thermostat

The first step in troubleshooting a furnace that is not kicking on automatically is to check the thermostat. Ensure that it is set to the desired temperature and that the fan is set to “Auto” instead of “On.” If the thermostat is programmable, double-check the settings to ensure that there are no conflicting schedules or temperature overrides.

2. Check the Power Supply

If the thermostat settings are correct, the next step is to check the power supply. Start by checking the circuit breaker or fuse box to see if the furnace’s circuit has tripped or blown a fuse. If so, reset the circuit breaker or replace the fuse. Additionally, check if the furnace is plugged in securely and that there are no loose connections.

3. Inspect the Ignition System

If the thermostat and power supply are functioning properly, the issue may lie with the furnace’s ignition system. Older furnaces often have a pilot light that needs to be lit manually. If the pilot light has gone out, consult the manufacturer’s instructions to relight it safely. Newer furnaces typically have an electronic ignition system that may require professional servicing if faulty.

4. Check the Air Filter

A clogged or dirty air filter can restrict airflow and cause the furnace to shut off automatically as a safety measure. Check the air filter and replace it if it appears dirty or clogged. Regularly replacing the air filter can improve the efficiency and lifespan of your furnace.

5. Inspect the Condensate Drain

If you have a high-efficiency furnace with a condensate drain, a clog in the drain line can cause the furnace to shut off. Check the drain line for any obstructions and clear them if necessary. Additionally, ensure that the condensate pump, if present, is functioning correctly.

6. Check the Gas Supply

If your furnace runs on natural gas or propane, ensure that the gas supply is turned on and that the gas valve leading to the furnace is open. If you suspect a gas leak, immediately evacuate your home and contact a professional for assistance.

7. Verify the Safety Switches

Furnaces have safety switches that detect issues such as a blocked flue or a dirty air filter. If any of these safety switches are triggered, the furnace will not start automatically. Check the safety switches, which are typically located near the blower motor or in the combustion chamber, and ensure they are not obstructed or faulty.

8. Consult the Furnace Manual

If you have followed the troubleshooting tips above and your furnace still does not kick on automatically, consult the manufacturer’s manual for specific troubleshooting steps. The manual may provide additional insights into the problem and offer solutions that are specific to your furnace model.

9. Contact a Professional

If all else fails, it is advisable to contact a professional HVAC technician. They have the expertise and tools to diagnose and repair complex furnace issues safely. Attempting to fix the problem without proper knowledge may result in further damage or voiding the furnace’s warranty.


A furnace not kicking on automatically can be a frustrating issue, especially during the cold winter months. By following the troubleshooting tips outlined in this article, you can identify the cause of the problem and take appropriate action to resolve it. Remember to prioritize safety and seek professional help if needed. Stay warm and comfortable throughout the winter season!