🛠️ Furnace Not Turning On? Here’s What Might Be Wrong
When your furnace is not turning on, it can be frustrating — especially during a Texas cold snap. Whether it’s a quick DIY fix or something that needs a technician, this guide covers the most common causes and how to troubleshoot before making a service call.
🔧 1. Thermostat Is Set Incorrectly
It sounds basic, but double-check that the thermostat is set to “heat” and the temperature is higher than the room temperature. Also, make sure it has working batteries.
🧠 Pro Tip: Switch it off and back on to see if it reboots the system.
⚡ 2. Tripped Circuit Breaker
Check your home’s breaker panel. If the furnace breaker is tripped, reset it once and listen for the furnace to click or start. If it trips again, call an HVAC tech immediately.
🔋 3. Clogged Air Filter
A dirty air filter can block airflow and cause the furnace to overheat and shut off.
📅 Filters should be changed every 1–3 months, especially in winter.
🔌 4. Pilot Light or Ignition Failure
Older gas furnaces use a pilot light. If it’s out, you’ll need to relight it following the unit’s instructions. Newer models use electric igniters which can fail over time and need replacement.
5. Blower Motor Problems
If the furnace turns on but no air is blowing, the blower motor may be burnt out or stuck. Check for unusual smells or sounds. You’ll likely need a tech for this one.
💻 6. Faulty Limit Switch or Control Board
Modern furnaces have safety switches and control boards that monitor temperatures. If any part fails, your furnace might lock out for safety reasons.
🧊 7. Frozen Condensate Line (in high-efficiency furnaces)
In colder temps, the condensate line can freeze, especially if it’s not insulated. This causes the furnace to shut down as a safety measure.
🔄 8. Furnace Lockout Mode
After multiple failed starts, some systems go into lockout mode. Turning the power off for 30 seconds and back on can sometimes reset the unit.
🛑 9. Gas Supply Issues
If you’re using gas, make sure the gas valve is on and your utility isn’t experiencing issues. You can also check other gas appliances to confirm gas is flowing.
The NFPA recommends having your heating system inspected annually to reduce the risk of fire hazards or equipment failure.
🔍 10. Furnace Age and Wear
Furnaces over 15 years old are more prone to breakdowns and inefficiency. If you’ve had multiple repairs in the past two years, replacement might be more cost-effective.
According to Energy.gov, clogged filters and poor maintenance are two of the top reasons furnaces fail to start.
📞 When to Call an HVAC Pro
If you’ve gone through these steps and your furnace still won’t turn on, it’s time to bring in a professional. Delaying could lead to frozen pipes, poor indoor air quality, or carbon monoxide issues in gas furnaces.
Need help now? Check out our Top HVAC Contractors in San Antonio for fast, trusted furnace repair.
✅ Final Thoughts
A furnace that won’t start can be caused by anything from a tripped breaker to a failed igniter. By going through this checklist, you can often avoid an unnecessary service call — or at least know what to expect before the technician arrives.