Carrier Furnace Not Blowing Hot Air? 4 Common Causes (+ Fixes)

Carrier is known for its high-quality furnaces, and if you own one, you’ve probably been very happy with how well it’s kept you warm. But like any other furnace, it may stop working due to neglected maintenance or old, worn-out parts. One of the more common issues is when it stops blowing hot air into your home.

Your Carrier furnace isn’t blowing hot air because it’s overheating, the pilot light is faulty, the thermostat is set too low, or the fan limit switch is faulty. You can get your furnace to blow hot air again by cleaning all parts, replacing broken ones, and setting a high temperature.

In this article, I’ll go over the most common reasons why a Carrier furnace isn’t blowing hot air. I’ll also discuss the appropriate fixes for each of these causes.

The Furnace Is Overheating

Your furnace is constantly generating heat through the burners. The burner flame allows air to be heated up, which is then blown into the ducts.

The furnace itself and your ductwork need to withstand this consistent heat — when things get too hot, problems can occur. A safety switch may trip in the furnace, causing the burner’s gas supply to shut off. 

There are a few reasons for overheating in a furnace, but a dirty air filter is the most common cause. The debris collected by the filter can block the airflow from the furnace toward the ducts, trapping the heat inside the furnace. This causes the internal temperature to rise and trip the safety switch.

How To Fix

Cleaning the filter is a pretty simple process:

1. Switch off the power to your furnace.
2. Remove the front panel. 
3. Remove the filter. 
4. Clean the filter thoroughly. If you have a disposable filter, throw it out and replace it. 
5. Make sure the replacement filter is fastened correctly. Put the furnace panel back on and switch the furnace on. 

If you need help locating, removing, and cleaning the furnace filter, take a look at the video below:

If cleaning the filter doesn’t fix the problem — or you’re uncomfortable with messing around in your furnace or don’t want to cause further issues — I recommend hiring a professional HVAC repairman to fix it.

Faulty Pilot Light

Older Carrier furnaces use a pilot light for ignition. The pilot light needs to be lit for ignition to occur. If the pilot light goes out, it means there will be no flame to ignite the gas coming from the burners. 

Multiple issues can affect the pilot light. Sometimes, you need to light it manually. Other times, it’s dirty or even broken.

If the pilot light is causing an ignition issue, you need to remove it, inspect it, and take appropriate action based on your findings. 

How To Fix

Start by checking whether the pilot light is lit. If you don’t see a flame on the pilot light, get a candle lighter to ignite it manually. You need a long-neck lighter so that you don’t have to push your hands into the furnace. 

If the lighter doesn’t create a flame on the pilot light, take a closer look to determine the problem. Here’s how to do this safely:

1. Switch the furnace off.
2. Open the combustion chamber.
3. Check for a build-up of debris on the pilot light. You may see some black residue from the flames and gases that pass through the area. 
4. If you find debris on the pilot light, clean it thoroughly. If cleaning it doesn’t fix the issue, move on to the next step.
5. Check for cracks and other signs of damage. If it’s damaged, remove and replace the pilot light.
6. When buying a new pilot light, make sure you buy a compatible one. You can use the model number on your current pilot light to ensure you get the right replacement.

The video below will give you an overview of how you can manually relight the pilot light:

Again, I recommend calling a local furnace repair expert if you’re uncomfortable with fixing the pilot light yourself.

Thermostat Is Set Too Low

If the temperature on your thermostat is lower than the room temperature, there’s no reason for your Carrier furnace to generate hot air. You might even get some air blowing from the ducts, but it’s only at room temperature rather than scorching hot.

How To Fix

Fixing this is a simple process. Here’s what you need to do:

1. Take a look at the fan settings. There are three options. Apart from ON and OFF, there’s an AUTO setting as well. If the fan is currently set to ON or OFF, switch it to AUTO. That’s because the fan will blow continuously if you set it to ON.
2. Look at the current temperature settings on the furnace. Is the temperature high enough so that the furnace has a reason to work? If the temperature is too low on the thermostat, turn it up.

Faulty Fan Limit Switch

If you’ve ruled out other issues mentioned in the article, the fan limit switch might be the problem.

The fan limit switch turns off heat when temperatures get too high in the furnace. The switch will also cause the fan to stop blowing air into your ductwork.

If the fan limit switch is faulty, there’s a chance that it turns the furnace off at inappropriate times. This may happen randomly, or you may find that the device isn’t pushing out any air at all.

The problem may lie with the connections of the fan limit switch, but perhaps the switch itself is broken. Like any other switch, the fan limit switch breaks as it gets older.

How To Fix

Here’s how to inspect the fan limit switch to see if it needs fixing or replacing:

1. Turn off your furnace.
2. Remove the front panel and locate the limit switch in the furnace. 
3. Make sure it’s installed correctly and hasn’t become loose.
4. If it seems secure, check for cracks, chips, or other signs of damage.
5. If you notice damage, or if the switch simply won’t work, replace it.

Ensure you get the same model to avoid potential compatibility issues.

If you want to replace the limit switch, watch the following video:

Summary

A Carrier furnace not blowing hot air often means there’s an issue with your thermostat settings. This is the easiest fix, but other problems can be at play too. You should consider the thermostat, fan limit switch, and other possibilities as well. 

If you’re uncomfortable making the repairs yourself or your furnace still isn’t working after attempting these fixes, I recommend calling a professional HVAC technician to fix it for you.