Seeing your furnace blowing cold air is frustrating, especially before winter in Boulder. The good news is many fixes are simple. Try these fast checks first, then call Mesa Plumbing if you want a pro to jump in.
First, Think Safety and Basics
Make sure the thermostat is set to Heat and the fan is set to Auto. If it is on On, the blower will run nonstop and can feel like cold air between heat cycles. Replace old thermostat batteries so settings do not drift. These quick moves clear a lot of air temp furnace problems.
Two-Minute Checklist to Stop Cold Air
1. Give the Furnace a Short Reset
Turn the thermostat to Off for one minute, then back to Heat. Some models need a brief cool down after a safety trip before they will fire again.
2. Check the Filter
A clogged filter starves airflow and overheats the system. The safety switch shuts the burner off and you end up with a house heater blowing cold air feeling. Swap in a clean filter and try a heat call again.
3. Close the Blower Door Fully
Many furnaces will not fire if the panel is loose. Press the door until it clicks. That tiny switch needs contact or the burner stays off.
4. Confirm Gas and the Flame Sequence
If you have a gas shutoff near the furnace, the handle should be in line with the pipe. When you call for heat you should see the inducer start, the igniter glow or spark, and then the burner light. If the burner lights then drops out after a few seconds, you likely have a sensor issue that needs a pro.
5. Look at Supply Vents
Make sure most vents are open. Too many closed vents can trip safeties and leave you with cool air from remaining registers.
Why the Air Feels Cold Even When It Is Working
Furnaces start by moving room air while the heat exchanger warms up. The first few seconds can feel cool. After a minute, supply air should feel clearly warmer than the room. If it stays chilly, the burner is likely not running or it is shutting off due to a safety condition.
Common Causes When Cold Air Persists
- Dirty flame sensor that makes the burner shut down early
- Clogged condensate line on high-efficiency units
- Pressure switch or venting issues after windy weather
- Limit switch trips from poor airflow due to a packed filter
- Thermostat mis wired after a recent battery swap or upgrade
If you have tried the quick list and still have a furnace blowing cold air, it is time for service. Mesa Plumbing can handle same-day fixes across Boulder and nearby mountain homes. Pre-winter prep is the best time to get ahead of surprise breakdowns.
When to Call Mesa Plumbing Now
- The burner will not light at all
- You smell gas or see scorch marks
- The furnace cycles on and off every minute
- You hear loud grinding or screeching from the blower
- Breakers are tripping
Need Help Fast?
Questions or maintenance due? Call Mesa Plumbing at (720) 680-2303 or schedule at www.mesaplumbing.com. We are ready for emergency response and fast heat recovery if your house heater is blowing cold air.
What to do if heater is blowing cold air
Start with the two minute checklist. Set the thermostat to Heat and Auto, replace the batteries, change a dirty filter, and make sure the blower door is fully seated. If the burner does not stay lit or the air never warms after a minute, call Mesa Plumbing for a safe diagnostic.
Why would a furnace blow cold air
Most often it is a safety shutoff from poor airflow, a dirty flame sensor, or a thermostat setting problem. You can also feel cool air during the first moments of a cycle while the heat exchanger warms up. If the room never heats, you likely have a burner or sensor fault.
How to fix a furnace blowing cold air
Confirm settings, replace the filter, and try a short reset by turning the thermostat Off for one minute then back to Heat. If that does not work, the fix usually involves cleaning or replacing a flame sensor, clearing a condensate line, or correcting vent and pressure issues. Those are best handled by a licensed tech.
Start with the two minute checklist. Set the thermostat to Heat and Auto, replace the batteries, change a dirty filter, and make sure the blower door is fully seated. If the burner does not stay lit or the air never warms after a minute, call Mesa Plumbing for a safe diagnostic.
Most often it is a safety shutoff from poor airflow, a dirty flame sensor, or a thermostat setting problem. You can also feel cool air during the first moments of a cycle while the heat exchanger warms up. If the room never heats, you likely have a burner or sensor fault.
Confirm settings, replace the filter, and try a short reset by turning the thermostat Off for one minute then back to Heat. If that does not work, the fix usually involves cleaning or replacing a flame sensor, clearing a condensate line, or correcting vent and pressure issues. Those are best handled by a licensed tech.
Do you have more questions about Furnace?
If your furnace problems keep coming back or you still feel a house heater blowing cold air, we can get the heat steady and safe for winter. Call 720 680 2303 or book at www.mesaplumbing.com.