Why Does My Furnace Blow Cold Air?

4 Troubleshooting Steps When a Furnace Stops Blowing Hot Air

The coldest days in Denver are some of the busiest for our team at DALCO Heating & Air Conditioning. Our experienced furnace repair technicians have dealt with about every type of problem that furnaces (and other heating systems) can run in to. Responding to a problem on a freezing day means they have to work quickly to get this vital system back up and running.

A furnace that stops blowing hot air can be alarming for any homeowner. It may even feel like the air conditioner is running. While that is almost definitely not the issue, there are several different reasons that can cause a furnace to blow cold air. But the good news is that this is something our team can often fix quickly! Many of the causes to this problem are relatively easy for us to diagnose and handle.

Furnace Blowing Cold Air: Time to Replace?

Trane furnace installed in Denver home by DALCO Heating & Air. Why does my furnace blow cold air?

Not necessarily. Just because your furnace is blowing cold air does not mean it is broken. Of course, that is always a possibility, especially if your furnace is 15+ years old. But there are a lot of reasons why a furnace can stop heating your home. And some of those issues may be something a homeowner can fix themselves!

DALCO Heating & Air Conditioning is on call here in the Denver area whenever you need a qualified repair technician to service your furnace. Call us anytime at 303-979-7541 – we are available for 24/7 emergency heater repair. However, before you call us, you may want to try out 4 troubleshooting steps to see if you can get the hot air flowing without needing an HVAC service call.

Why Does My Furnace Blow Cold Air: 4 Troubleshooting Steps

Some easy-to-fix problems can cause a furnace to stop blowing hot air. Here are four troubleshooting steps a homeowner can try to possibly solve the problem on their own.

# 1: Is Your Thermostat Set Correctly?

Thermostat set for 68, something to check when your furnace is blowing cold air

It’s very common for different people sharing spaces to have different ideas on what the best temperature should be. You may find that someone in your household simply lowered the thermostat setting without telling you.

Is the temperature set to be warmer than it already is inside? If not, then just turn the temperature up several degrees.

Hopefully, this was your only problem and you’ve already solved your heating issue! Of course, that probably means you are now facing a sort of “thermostat war” with someone else in your home. Unfortunately, we don’t have any troubleshooting steps for that.

#2: Is the Fan Set to On?

While you’re still at the thermostat, see if the fan is ON. If it’s set to ON, your blower will be running all the time. That could be what is causing you to feel cool air coming out your vents. Why? If your indoor air is already at the set temperature, your furnace will not be warming any more air. So, compared to the air in your home, that blown air can feel cold.

Just put the fan to AUTO so that the blower fan only runs when the furnace is heating the air.

#3: Is Your Air Filter Dirty?

Dirty air filter being pulled out of a furnace that is not blowing hot air

Even if you think it is not time yet to change your air filter it might be. It’s quite common for people to be wrong with how often they need to change their filter. The result is a furnace running with a dirty filter and that can cause a wide variety of problems, including (you guessed it) making it feel like cold air is blowing out of your furnace.

A dirty furnace filter can restrict air flow and possibly cause the furnace’s heat exchanger to overheat, which can be a very dangerous situation. A cracked heat exchanger has the risk of a potential carbon monoxide leak.

Some furnaces have internal sensors to detect potential dangers like this and will shut down as a safety precaution. You won’t be able to get your furnace back up and running until that potential problem is resolved AND your furnace stops automatically shutting down.

If you see that you do have a dirty air filter, change it. That may resolve the problem. However, if the furnace stopped because of a safety precaution function, it will not come back on automatically. It will likely need to be reset. Call DALCO at 303-979-7541 and our repair technicians will fix whatever issue your furnace is having and safely get it working again. We provide service to the entire Denver metro area.

# 4: Is Your Furnace Lit?

Has the furnace light gone out? Take a look at the burners and see if there is a flame burning.

To relight your pilot light, first you should turn the thermostat from HEAT to OFF. Then turn the control knob at your furnace to PILOT. If it was set to ON, turn it OFF and wait 5 minutes to allow any potential gas to clear out.

After that wait, turn the knob to PILOT and push it in. You can expect to hear gas flowing to the burner. While you continue pushing in the knob, put a flame to the pilot opening. Once you see it light up, you will release the knob slowly and then turn it to ON. Be sure to go back to your thermostat and turn it to HEAT. You should feel warm air again rather quickly after that.

Important Safety Notice: If you smell gas after waiting 5 minutes, there is a possibility of a gas leak. Do not relight your furnace if you smell gas. Contact a professional technician to come out and safely get it back running.

Call DALCO for emergency furnace repair

Other Possible Cold Air Causes

In addition to these issues that you can troubleshoot, there are a variety of other reasons why a furnace may stop blowing hot air. Many of those problems are beyond a homeowner’s ability to handle on their own.

Other Heater Issues Include:

    • Gaps in the duct work
    • An electrical problem with the ignitor
    • Dirty flame sensor in the furnace
    • Out of fuel (oil furnace)

When to Call a Professional HVAC Company

If you try these 4 troubleshooting steps and your furnace still does not blow hot air, contact a qualified heating repair technician. DALCO Heating & Air Conditioning has repaired furnaces in the Denver area since 1981. We are experienced and trained to repair any type or model of heating system. Call us for quick professional service at 303-979-7541.

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