When the temperatures drop, the last thing you want is for your furnace to start blowing cold air instead of keeping your home warm and cozy. If you’ve noticed this issue, don’t panic—there are several common reasons why it may be happening. Some fixes are simple, while others may require professional repairs.
1. Thermostat Issues
Your thermostat controls the temperature and operation of your furnace. If it’s set incorrectly, it could cause the furnace to blow cold air.
How to check:
✅ Ensure the thermostat is set to “Heat” and not just “Fan.”
✅ Check that the fan setting is on “Auto” instead of “On.” The “On” setting keeps the blower running even when the furnace isn’t actively heating.
✅ If the thermostat runs on batteries, replace them.
Solution: Adjust the thermostat settings and replace batteries if needed.
2. Overheated Furnace (Safety Shutoff Triggered)
If your furnace gets too hot, it may trigger a safety shutoff to prevent damage. This can happen due to dirty air filters restricting airflow.
How to check:
✅ Inspect the air filter—if it’s dirty, it could be blocking airflow and causing overheating.
✅ If your furnace turns on, blows warm air briefly, then switches to cold air, it may be shutting down due to overheating.
Solution: Replace the air filter and ensure vents and registers are not blocked. If the issue persists, a technician may need to inspect for deeper airflow problems.
3. Pilot Light or Ignition Problems
Gas furnaces rely on a pilot light or electronic igniter to heat the air. If either fails, the furnace may blow cold air.
How to check:
✅ If your furnace has a pilot light, see if it’s out.
✅ If your furnace uses an electronic ignition, a malfunction could prevent heating.
Solution: If you’re comfortable doing so, try relighting the pilot light following your furnace manual’s instructions. For ignition system failures, call a professional for repairs.
4. Gas Supply Issues
If your furnace isn’t getting enough gas, it won’t be able to produce heat.
How to check:
✅ Make sure the gas valve is fully open.
✅ If you have other gas appliances (stove, water heater), check if they’re working.
✅ If none of your gas appliances are working, you may have a gas supply issue—contact your utility company.
Solution: If the gas is off or weak, check with your gas provider. If the issue is isolated to the furnace, a technician can inspect the gas valve or burners.
5. Ductwork Leaks or Blockages
Even if your furnace is producing warm air, leaks in your ductwork can cause cold air to mix in before it reaches your vents.
How to check:
✅ Feel around duct joints for noticeable air leaks.
✅ Check if some rooms are colder than others.
Solution: Seal duct leaks with foil tape or have a professional inspect and repair ductwork.
6. Faulty Limit Switch
The limit switch controls when the blower turns on and off. If it malfunctions, it may leave the fan running continuously, blowing cold air.
How to check:
✅ If the blower runs non-stop, even when the furnace isn’t heating, the limit switch may be faulty.
Solution: A professional can test and replace a faulty limit switch.
When to Call a Professional
If you’ve checked your thermostat, filter, and pilot light but still have cold air coming from your furnace, it’s time to call a furnace repair expert. A certified HVAC technician can diagnose issues with your furnace’s gas supply, ignition system, ductwork, or internal components.
At Platinum Plumbing & Heating, we provide fast, reliable furnace repair services to get your home warm again. Contact us today for expert heating solutions!
