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Furnace not blowing hot air? The cause is usually the thermostat setting, a clogged air filter, or a burner that will not light. Many of these you can check in a few minutes. If the simple checks do not fix it, a licensed tech can handle furnace repair in Claremore safely, often the same day.
The first cold snap of the year is when we get the most of these calls in Claremore, Tulsa and Owasso. Below are the 7 things to check, what each one means, and when to stop and call. If your house is cold right now, call Cool Down Heating and Air at (918) 527-6792. We answer 24/7.
Key Takeaways
- Fan set to ON is the number one reason a furnace blows cool air between heating cycles. Set it to AUTO.
- A dirty filter can trip a safety switch that shuts off the burners while the blower keeps running.
- Ignition problems like a dirty flame sensor cause the burners to light and then shut off after a few seconds.
- Heat pumps blow cooler air than gas furnaces, and a short cool blast during defrost is normal.
- Smell gas? Leave the house first and call your gas utility from outside.
Safety First Before You Touch Anything
A gas furnace burns fuel inside your home, so a few rules come before any troubleshooting. If you smell rotten eggs or sulfur, do not flip switches or try to relight anything. Get everyone out and call your gas company from outside. If your carbon monoxide alarm sounds, leave the house and call 911.
Make sure you have a working CO alarm near every sleeping area. The federal carbon monoxide safety center explains where to place alarms and the warning signs to watch for. A cracked heat exchanger or blocked vent can leak CO without any smell, which is why a yearly inspection matters.
7 Things to Check When Your Furnace Blows Cold Air
Work through these in order. The first three solve a large share of no-heat calls, and none of them need tools.
1. The Thermostat Mode and Fan Setting
Set the thermostat to HEAT and raise the temperature 3 to 5 degrees above the room temperature. Then check the fan. If it is set to ON, the blower runs all the time, even when the burners are off. That pushes room-temperature air through the vents, which feels cold on your hand. Switch it to AUTO so the fan only runs when the furnace is heating. A blank screen usually means dead batteries.
2. The Air Filter
A clogged filter is the most common cause we find in the first weeks of heating season. When air cannot move through the filter, heat builds up inside the furnace. A safety part called the high-limit switch senses that heat and shuts off the burners to protect the furnace. The blower often keeps running to cool things down, so you get cold air from the vents. Swap the filter, wait a few minutes and try again.
3. Power and the Furnace Switch
Most furnaces have a switch on or near the unit that looks like a light switch. It is easy to bump it off while storing things nearby. Check that it is on, and check the breaker panel for a tripped furnace breaker. Also make sure the front panel of the furnace is fully closed. Many furnaces have a door switch that keeps the unit off when the panel is loose.
4. The Gas Supply
If other gas appliances like the water heater or stove work, gas is reaching the house. Next, look at the gas valve on the line going into the furnace. The handle should line up with the pipe when it is open. If it sits across the pipe, it is closed. If you are not sure, leave it alone and call a pro. Never force a stuck gas valve.
5. The Igniter or Pilot Light
Older furnaces have a standing pilot light, a small flame that stays lit all the time. If it went out, the burners cannot light. Follow the relighting steps printed inside the furnace door, and only if you are comfortable doing so. Newer furnaces use an electronic igniter that glows bright orange before the burners light. If you hear the furnace try to start but never see that glow, the igniter may be cracked or worn out. That is a common, fairly quick repair for a tech.
6. The Flame Sensor
This is the classic “it lights, then shuts off” problem. The flame sensor is a thin metal rod that confirms the burners are lit. When it gets coated with soot, it cannot sense the flame. The furnace thinks the burners failed and shuts off the gas after a few seconds. It will often try three times, then lock out. Cleaning or replacing the sensor usually fixes it, but it means opening the burner compartment, so most homeowners call a pro.
7. Error Codes, Drain Lines and Vents
Most modern furnaces have a small window with a blinking light on the control board. The blink pattern is a code, and the chart is usually printed on the inside of the door. Write it down before you call, because it saves time. High-efficiency furnaces also have a condensate drain and plastic vent pipes. A clogged drain or a vent blocked by leaves or a bird nest will trip a pressure switch and stop the heat.
Match the Symptom to the Cause
This table helps you describe the problem when you call. A clear description often means the tech brings the right part on the first trip.
| What you notice | Likely cause | DIY or pro? |
|---|---|---|
| Cool air between heat cycles | Fan set to ON | DIY |
| Burners shut off, blower keeps running | Dirty filter tripping high-limit switch | DIY first, then pro |
| Burners light, then shut off in seconds | Dirty flame sensor | Pro |
| Clicking but no flame | Igniter or gas valve problem | Pro |
| Nothing happens at all | Power switch, breaker, door switch or thermostat | DIY check, then pro |
| Blinking light on control board | Stored error code | Note the code, then pro |
| Water near a high-efficiency furnace | Clogged condensate drain | Pro |
Heat Pump Owners: This May Be Normal
A lot of homes in Claremore, Verdigris and Catoosa heat with a heat pump instead of a gas furnace. Heat pumps warm your home by moving heat from outside air, and the air from the vents is usually around 90 to 100 degrees. A gas furnace often sends out much hotter air. So heat pump air can feel cool on your hand even when it is working fine.
On cold, damp days, a heat pump also runs a defrost cycle to melt frost off the outdoor coil. During defrost you may see steam outside and feel a short burst of cooler air inside. That is normal. What is not normal is cool air that never warms up, ice that covers the whole outdoor unit, or emergency heat running all the time.
When to Stop and Call a Pro
Some signs mean you should not keep resetting the furnace. Call a licensed technician if you notice any of these:
- A gas smell, or a CO alarm going off
- The furnace locks out after three start attempts
- A burning, electrical or dusty smell that does not go away after the first day of heating
- Loud booms, bangs or screeching when the burners start
- Yellow or flickering burner flames instead of steady blue
- A breaker that trips again after one reset
If any of these sound familiar, call us at (918) 527-6792. We will tell you what is wrong in plain English and give you a written price first. Our furnace repair cost guide shows typical prices for the repairs on this list so you know what to expect.
Repair It or Replace It?
Most furnaces last around 15 to 20 years with regular care. An igniter, flame sensor or filter problem is worth fixing on almost any furnace. A cracked heat exchanger or a failed control board on an older unit is a different story, because those repairs cost more and the furnace may not have many years left.
Efficiency is part of that choice. Furnace efficiency is measured by AFUE, which is the share of fuel that turns into heat for your home. Older furnaces with a standing pilot and a natural draft waste much more fuel than newer models, which can mean higher gas bills every winter. You can compare newer models with the ENERGY STAR furnace ratings before you buy. If your furnace is near the end of its life, see our new furnace cost breakdown before you decide.
How to Prevent a No-Heat Call This Winter
Most no-heat calls in December start with a small problem nobody noticed in October. A few simple habits help:
- Test the heat early. Turn it on for an hour in late September or early October, before you actually need it.
- Change the filter at the start of the season and every 1 to 3 months after that.
- Clear the vents and the area around the furnace. Keep boxes and paint cans at least a few feet away.
- Book an annual furnace tune-up visit. A tech cleans the flame sensor, checks the igniter and tests for CO and gas leaks.
Furnace Not Blowing Hot Air FAQs
What does it mean if the furnace is blowing cold air?
Cold air from a furnace usually means the blower is running but the burners are not lit. The most common reasons are a fan set to ON, a clogged filter tripping the high-limit switch, a dirty flame sensor or a failed igniter. Check the thermostat and filter first.
What is a high limit switch on a furnace?
The high-limit switch is a safety part that shuts off the burners if the inside of the furnace gets too hot. It most often trips because of a dirty filter or blocked vents. If it trips often, the furnace needs service before the part or the heat exchanger is damaged.
What does a dirty air filter do to a furnace?
A dirty filter cuts airflow, so heat builds up inside the furnace. That can trip the high-limit switch, shorten the life of the blower motor and, over time, stress the heat exchanger. It also raises your gas bill because the furnace runs longer to heat the house.
Why is my furnace running but not producing heat?
If the furnace runs but produces no heat, the burners are not lighting or staying lit. Look for a closed gas valve, a pilot light that went out, a bad igniter or a dirty flame sensor. A blinking error code on the control board will usually point to the exact part.
How long do furnaces usually last?
Most gas furnaces last about 15 to 20 years. Yearly maintenance, clean filters and good airflow help a furnace reach the top of that range. Frequent repairs, rising gas bills and uneven heat are signs one is close to the end.
Get Your Heat Back On in Claremore
If you have checked the thermostat, the filter and the power and your furnace still blows cold air, it is time for a diagnostic. Call Cool Down Heating and Air at (918) 527-6792. You will get honest answers, a written price before any work, and a free second opinion if another company told you to replace. You can also reach our Claremore team online. We serve Claremore, Tulsa, Owasso, Catoosa, Verdigris, Collinsville and Broken Arrow, day or night.
Cool Down Heating and Air
24606 US RTE 66 #4, Claremore, OK 74019
Phone: (918) 527-6792
Hours: Open 24/7
Oklahoma License #099177 | Owner: Ricky Roberts | Serving Green Country since 2019
Service area: Claremore, Tulsa, Owasso, Catoosa, Verdigris, Collinsville, Broken Arrow and nearby areas
