Have you ever walked into your home on a cold night, only to realize your furnace is blowing cold air? Many homeowners would find this alarming. In many cases, the cause is something minor you can troubleshoot in just a few minutes. In some cases, it could be a problem that’s best handled by an HVAC expert.
Reasons Why Your Furnace Is Blowing Cold Air
Noticing that your furnace is blowing cold air? This issue could be caused by a number of issues, including:
- Incorrect thermostat settings
- Closed supply vents
- Dirty air filter
- Furnace hasn’t warmed up yet
- Faulty gas valves and pilot light
- Faulty fan limit switch
- Faulty flame sensor
Let’s take a closer look at each of these potential causes.
Incorrect Thermostat Settings
It’s helpful to think of a thermostat as your furnace’s control panel. It regulates the temperature in your home and turns the furnace on and off as needed. If the settings are incorrect, your furnace may not produce heat.
If you think your thermostat’s settings might be the problem, here’s how to reset it:
- Select “Heat” mode on the thermostat
- Switch the fan from “On” to “Auto”
Wait 10 minutes to see if this fixes the problem. If it doesn’t, proceed to the next solution.
Closed Supply Vents
Your furnace supplies air to your home through multiple vents. Too many closed vents disrupt airflow and can lead to uneven heating. In some situations, this can trigger a safety mechanism in your furnace, causing it to shut down or blow cold air.
Follow these steps to fix closed supply vents:
- Locate all the air supply vents in your home.
- Inspect them to confirm airflow when your furnace is running.
- Remove blockages like furniture, rugs and other household items.
Dirty Air Filter
Furnaces rely on clean airflow to heat your home, and an air filter does a lot of the heavy lifting. It catches dust, pet hair and whatever else might be floating around. But if the filter gets clogged, warm air can’t move through.
You can replace a dirty air filter by following these steps:
- Turn off your furnace.
- Find the air filter. It’s usually in a metal tray inside the blower compartment.
- Pop it out and inspect it. Discard it if it’s dusty or clogged.
- Grab a replacement with the same size and swap it in. Make sure the arrow on the filter points toward the furnace.
It’s a quick fix, but it can make a big difference in how well your furnace runs.
Furnace Hasn’t Warmed Up Yet
Sometimes, your furnace may take longer to warm up. This usually occurs after a few weeks or months of inactivity. The next time you turn it on, it may blow cold air for the first few minutes until the burners ignite.
Waiting it out is your best option. Then, follow these troubleshooting steps if your furnace keeps malfunctioning after 10 minutes:
- Double-check your thermostat settings for accuracy
- Restart the furnace
Faulty Gas Valves and Pilot Light
A problem with your gas valve or pilot light can keep your furnace from producing heat. If your system isn’t receiving gas or the pilot light won’t stay lit, your furnace may blow cold air or shut down.
Keep an eye on the burner flame. If it’s flickering or won’t stay lit, turn off the furnace and call in an HVAC technician.
Faulty Fan Limit Switch
The fan limit switch regulates when the blower fan turns on or off. Even when your furnace isn’t producing heat, the blower may continue to run if the switch is faulty.
Contact an HVAC expert to inspect and repair it.
Faulty Flame Sensor
Your furnace has a safety device called a flame sensor. Its job is to make sure there’s actually a flame when the burners switch on. If it doesn’t sense one, it shuts everything down to prevent gas from building up.
Sometimes, the flame sensor gets dirty and stops working properly. When that happens, it might fail to detect a flame even if your burners are working, causing your furnace to blow cold air or shut off.
It’s best to have an HVAC expert handle a faulty flame sensor. They’ll locate the sensor, clean off any grime or buildup, reinstall it and restart your furnace to see if that resolves the issue.
Why Is My Furnace Not Responding to the Thermostat?
There are several reasons why your furnace is not kicking on when the temperature drops. The issue might be with the following:
- Dead batteries
- Malfunctioning thermostat
- Incorrect settings
Let’s go over these in more detail.
Dead Batteries
If your thermostat is battery-powered, a dead battery can disrupt its connection with the furnace. It won’t be able to send signals to the furnace to turn on or off, causing it to blow cold air. Replacing your batteries may fix the issue.
A Malfunctioning Thermostat
Sometimes, the problem is with the thermostat itself. A faulty thermostat sends the wrong signals to your furnace or sends nothing at all. As a result, the furnace may fail to respond when you adjust the temperature.
Incorrect Settings
A simple mistake, like an incorrect temperature setting, can cause heating issues. For instance, if your thermostat is set to “Cool” instead of “Heat,” your furnace won’t turn on. Also, if you set the fan to “On” instead of “Auto,” it might run continuously, even when the furnace isn’t heating.
Can a Low Battery in a Thermostat Affect the Furnace?
A weak battery can prevent the thermostat from connecting with the furnace. This can lead to inaccurate temperature readings, inconsistent heating and complete failure of the heating system.
Don’t Ignore Low Battery Warnings
Check for low battery indicators to ensure a smooth connection between the furnace and the thermostat. That way, you’ll prevent your HVAC unit from shutting down unexpectedly.
How to Check for Low Battery Indicators
To see if your battery is low, here are some signs to check:
- A flashing light
- Text on the display
- A light that turns on when your battery is low
- Beeping noises
- A blank display
If your thermostat suddenly stops working, a low battery might be the culprit. Find the battery compartment and replace the old battery with a new one. After that, give your thermostat a few minutes to reset and start functioning normally.
When to Call in an HVAC Pro
Dealing with a faulty furnace can feel overwhelming. While you can tackle quick fixes like a battery change or an air filter replacement, some issues are best left to an HVAC expert.
ABC Can Solve Your Heating And Cooling Woes
Furnaces are complex systems, and trying to work on them without special training and tools can create larger problems and can even lead to damage to your home. Instead of taking these risks, contact the professionals at ABC Home & Commercial Services. Our licensed specialists are available all day and all night to handle any HVAC repairs or issue you may be having.
