Why Is My Furnace Blowing Cold Air?
When the temperatures drop in Missouri, the last thing you want is a furnace that’s pushing out cold air. The good news? In many cases, it’s not a total system failure, just a small issue you can identify (and sometimes fix) yourself before calling a pro.
1. Check Your Thermostat Settings
Sometimes the culprit is as simple as your thermostat being on the wrong mode.
Make sure the setting is on HEAT, not ON or COOL.
If the fan is set to “ON,” it’ll blow continuously, even when the furnace isn’t heating. Switch it to AUTO so the fan only runs when heat is produced.
🧰 Pro Tip: If you use a smart thermostat, check for firmware updates or low batteries.
2. Replace a Dirty Air Filter
A clogged air filter restricts airflow, forcing your furnace to overheat and shut off the burners as a safety measure, while the fan keeps blowing.
Pull the filter and hold it up to the light. If you can’t see through it, replace it.
Change filters every 30–90 days, especially during Missouri’s winter months when systems run more often.
🧠 Pro Insight: Restricted airflow is one of the top reasons homeowners in Chesterfield call for “no heat” service calls in January.
3. Inspect the Pilot Light or Igniter
If your furnace uses a pilot light:
Make sure it’s lit. If it isn’t, follow your manufacturer’s instructions to relight it.
For modern electronic ignition systems:You may hear the furnace trying to start but failing, a sign the igniter needs replacement.
⚠️ If you smell gas or the pilot won’t stay lit, shut the system off and call a professional immediately.
4. Examine the Flame Sensor
A dirty or corroded flame sensor can make your furnace think there’s no flame, causing it to shut off the gas and keep the fan blowing.
Cleaning or replacing the flame sensor usually resolves this, but it’s best handled by a licensed technician.
5. Check for Duct Leaks
In older Chesterfield homes, leaky ductwork can cause warm air to escape before it reaches your vents.
Inspect visible ducts for gaps, loose joints, or holes.
Proper sealing can improve airflow and reduce energy bills.
6. When to Call a Professional
If you’ve checked these basics and the problem persists, it’s time to bring in a pro. Issues like failed limit switches, blower motor problems, or gas valve malfunctions require diagnostic tools and expertise.
At Fresh Air Heating & Cooling, our certified technicians have been keeping Chesterfield and St. Louis homes warm for over 30 years. We offer same-day furnace repair, safety inspections, and honest solutions.
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Don’t wait for your furnace to quit on the coldest night of the year.