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Bundling up in blankets by the fire during a cold winter’s night sounds fun and cozy.  However, when your furnace isn’t blowing warm air and the blankets become a necessity to keep warm, it’s less than ideal. Your furnace is essential on cold winter days and when it starts blowing cold air you want to fix it fast.

Here are the main reasons a heater may be blowing cold air and some DIY fixes:

#1. Pilot Light Problem

Older gas furnaces still use a pilot light to ignite a flame in the furnace and start the heating process. If you have a furnace that is 10+ years old, you’ll want to check here first. Newer, high efficiency furnaces no longer use a pilot light system.

You’ll want to consult your furnace manual for the most accurate information in finding your pilot light and how to relight it. Typically, the pilot light will be somewhere near the bottom of the furnace. If you do find the pilot light is out, then it is possible to relight it yourself.

  • First, turn your furnace off
  • Second, wait at least 5 minutes
  • Third, turn your furnace switch from “off” to “pilot”
  • Finally, hold down the rest button and relight the pilot light at the same time. You will need to use a long-stemmed lighter to reach the pilot. Once the pilot light is lit, then you can release the reset button.

You’ll want to make sure the pilot light stays lit. If it does not, then it’s time to call for professional furnace repair.

#2. Dirty Flame Sensor

flame sensor cleaning tune up

Another reason a furnace may be blowing cold is a dirty flame sensor. The flame sensor is a small metallic rod that sits in front of the flame inside the furnace. Its job is to do exactly what the name suggests – tell the furnace that there is a flame. It does this so that an overabundance of unburned gas does not build up inside the furnace. So, if the flame sensor doesn’t detect a flame within seconds of the furnace starting up, it will shut down. If the flame sensor is dirty, then it will be unable to detect the flame quickly. Most often buildup on the sensor is the issue, but it is possible the flame sensor could also be broken.

We do not recommend attempting to clean your own flame sensor unless you are somewhat familiar with the inner workings of the furnace. If you do want to attempt to clean it, please make sure to shut the power to the furnace off first and know you will need a screwdriver to remove the sensor.

Cleaning the flame sensor is part of our standard furnace maintenance. Check out our Total Care Club Super Savings Plans to learn more.

 #3. Dirty Air Filter

dirty air filter hvacYour furnace filter helps ensure that the air recirculating through your furnace is clean. When they get clogged with particles like dust and dander, it can restrict the airflow to your furnace, causing it to blow cold air. The same is true if you have chosen a filter with a very high MERV rating, mean they are thicker and filter out even smaller particles. Although this sounds like a great idea, if the filter is too think it can cause your furnace to work too hard to pass air through that filter. We recommend a MERV rating of 11 for most homes.

Before calling for furnace service, check your filter to see if it’s dirty. If you cannot see through the filter, then the filter needs changed. Swap out the filter and give it about an hour to see if the airflow has improved and the furnace is blowing warm air once again.

READ MORE: How often to change furnace filter.

#4. Lack of Gas Supply

The gas valve is the part that is responsible for bringing gas from the supply into the furnace itself. If your furnace isn’t getting enough gas supply due to an issue with the gas line or a bad gas valve, then it may cause your furnace to blow cold air. Due to the danger of working with gas and expertise needed to diagnose this issue, an HVAC company should be called out if you suspect this might be the issue.

#5. Thermostat Fan Settings 

thermostat fan settings menu

If your thermostat fan is set to ON instead of AUTO then you may feel cold air coming from your vents. This is because the fan is running, but the furnace isn’t currently heating the air. This is normal and not a cause for alarm. If you’d prefer to not feel air circulating at all times you can set the thermostat fan back to AUTO and you will only feel air coming out when the furnace is actively heating the air.

If you have a programmable or WiFi thermostat, then you will change your fan settings within your thermostat app or by finding the settings menu on your digital thermostat display.

If you have a traditional, non-programmable thermostat, then there will most likely be a toggle switch for the fan settings on the thermostat.

#6. Clogged Condensate Lines

High efficiency furnaces have something called a condensate line. Condensate lines transfer water away from the unit. If this line gets clogged, the furnace won’t ignite due to the system’s overflow kill switch that prevents water damage. If this is the issue, then you will most likely see standing water around the furnace as well.

A clogged condensate drain is caused from sediment buildup in the pipe. You can try to vacuum this out yourself if you have a wet/dry vacuum or you can also use a garden hose to try to wash out the buildup by placing the hose in the drain opening on the furnace drain pain.

Help for Furnace Blowing Cold Air

If you are in the Cincinnati area or other part of southwestern OH and your furnace is blowing cold air, give Quality Comfort a call or book service online 24/7!