Furnace Blows Cold Air: Troubleshooting Tips

Why is cool air coming from my vents?

The middle of a cold winter is the worst time for a furnace to break down. The coldest days are some of the busiest for our repair technicians at Steve’s Heating & Cooling. Fortunately, our team has encountered just about every possible problem a heater can have and can often get a furnace quickly back up and running.

One of the most alarming problems a homeowner can experience is cold air coming out of their vents. It may even seem like your air conditioner is suddenly running. Instead, what is probably happening has nothing to do with your air conditioning. Fortunately, when a furnace appears to be blowing cold air, it’s a problem that can usually be fixed.

What to do when you find your furnace blows cold air

Don’t assume the cold air means your furnace is broken. That may be the case, especially if you have an older furnace, but there are a lot of other reasons why there isn’t warm air coming through your vents. And many of those reasons are easy for just about anyone to address on their own.

Four Steps to Troubleshoot a Furnace that blows cold air

Step 1: Is the thermostat set Correct?

Make sure that your thermostat is set to be warmer than the current temperature.

Change the temperature to several degrees below the ambient temperature and make sure it’s on the WARM setting. If everything is working fine, your furnace should start to heat your home.

Step 2: Check the Thermostat Fan

Is the FAN set to ON? Having the blower running all the time could cause this problem. Air will still be coming through your vents even when the furnace isn’t heating. Compared to the existing temperature, it probably feels cold.

Turn your fan setting to AUTO. This AUTO setting will have the blower fan running only when the furnace is heating the air.

Step 3: Change a Dirty Air Filter

A dirty furnace filter may block sufficient airflow, which can then cause the heat exchanger to overheat. This can cause dangerous problems that may even lead to a carbon monoxide leak, so a furnace may shut off its burners as a safety precaution.

Check your air filter and change it if it is dirty. It is possible you will still need to reset the furnace to start working again. Because of the potential danger of a cracked heat exchanger, you should call a professional heating repair technician to ensure the furnace can turn on safely.

Step 4: Check the Pilot Light

If you have a gas furnace with a pilot light, you may find that it is not lit. Check where your burners are to ensure a flame is still burning.

Relight your pilot light. To do this, turn your thermostat from HEAT to OFF so the furnace won’t come on immediately when you light it. Turn the control knob to be set on PILOT. If the knob is already ON, turn it to OFF and wait about five minutes so that any gas can get cleared out.

Safety Note: If you notice the smell of gas after waiting several minutes, you may have a gas leak somewhere. Do not attempt to light or turn on your furnace if you smell gas. Call a professional technician to come out and ensure it can be relit safely.

After waiting those 5 minutes, turn the knob to PILOT and push it in. You should hear the sound of gas flowing. Put a flame to the pilot opening as you continue pushing in the knob.

When you see the pilot light, slowly release the knob and turn it ON. You can turn your thermostat back to HEAT, and your furnace should start blowing warm air.

When do you need a Professional Furnace Repair?

If none of these troubleshooting steps fix the problem with your heating system, you may have an issue that requires a professional furnace repair technician.

Call Steve’s Heating & Cooling at 816-436-8475.

We can repair and service any type or model of furnace or heating system. We have great reviews and are the HVAC team that people across Kansas City call to keep their homes warm every winter.