It’s always a smart idea to check your heating system before it turns cold outside. This can signal any type of issues before your minor heating and air problem becomes an emergency call. “I just tested my heat in expectation of the colder weather setting in, but my furnace is blowing cold air” is a common complaint that heating and air companies in Knoxville hear often in the Fall.

While your furnace or heating unit blowing cold air could be a quick fix, it might also be a sign of more serious problems requiring a certified heating and air technician to further assess and fix the issue. Here are a few reasons why your furnace could be blowing cold air and when you should call in professional help.


The simplest solution to assess and fix if your furnace isn’t blowing hot air is that your pilot light has gone out. The pilot light is a small flame inside of your furnace that is used to ignite the burners that then heat up the air circulated throughout your home. Pilot lights can go out for several reasons, including an inefficient flame that burns yellow instead of blue, a malfunctioning thermocouple, dirt or dust around your pilot light, or even a strong draft around where your furnace is located. While in the majority of cases your pilot light going out is a one-time thing that can be fixed by following the procedure to relight, if your pilot light continues to go out, it could allude to bigger problems that require a certified technician to replace a certain part of your heating and air conditioning system.


If you have ensured that your pilot light is indeed on, then the next reason for the furnace blowing cold air could be your thermostat. Thankfully, it’s easy to troubleshoot the thermostat yourself to discover if it is working properly or not. First, make sure that the temperature on your thermostat is set significantly higher than the room or it won’t trigger the heating system. Additionally, check that your fan switch is set to “Auto” and not “Off”. If the fan is set to “On” it will blow air regardless of what temperature your thermostat is registering.

If you have a thermostat that runs on batteries only and they are running low, this will affect the thermostat’s ability to engage the correct temperature inputs and, thus, blowing cold air. By sliding the thermostat’s control panel of its base on the wall you can check if it does indeed run only on batteries or if it has a battery backup or if it connected to the main power in your home. If it runs solely on batteries, try to swap them out for a fresh set and try to set the temperature to see if the hot air kicks on.


Damaged ductwork can cause the warm air cycling up from your furnace to leak out into your basement or attic and cause cold air to come out of your registers instead. Holes in your ductwork may be difficult to diagnose, depending on where your ductwork is located, but should be checked for damage. Damage can result from the sheer age of your ductwork or outside influences. Repairing damaged ductwork can require simple special thermal duct tape or may require a complete replacement of a section of your ductwork.


Your flame sensor is a major component inside your furnace. This is essentially a wire that sticks inside the flames of your burners to ensure the flame has made it across each burner. Sometimes your flame sensors can become dirty or will need to be replaced and this can cause cold air to blow out of your registers. While you may be able to simply take these out and clean them to troubleshoot, if you need to replace the flame sensors, you may need to contact a qualified service technician to locate and install the new parts for you.


Newer heating and air systems utilize a nitrate ignitor versus the standing pilot lights. If you have a faulty ignitor that needs to be replaced, it’s most likely that you’ll need to contact a heating and air technician to find the right part and to install it into your heating system.


If you have an older oil furnace or boiler that is blowing cold air, it may be that your oil filter needs to be replaced. Furnaces that run on oil have a filter that is like your car’s which keeps contaminants like oil and dust out of the heating system. If the oil filter becomes clogged with debris, it can cause your system to blow cold air even with the heat engaged. The oil filter will need to be changed out to solve the cold air problem. If your system does have an oil filter, it looks very similar to a car’s oil filter and only require basic tools like a wrench to remove. If you don’t feel comfortable changing out your oil filter, you can contact a heating and cooling company near you who can change it out for you.


If your pilot light continues to go out, your thermostat has power but doesn’t seem to work properly, or you can’t locate the reason for why your furnace is blowing cold air, it is time to call the professionals to help you get your warm air back on and working. Always keep in mind that your heating and air system is connected to your electrical system, and in gas systems, your gas lines to the house as well. With safety in mind, it’s always better to contact an experienced heating and air company to send a certified technician to fix a problem with your furnace or heating and air system.

City Heating and Air has been repairing HVAC Systems in Knoxville and the surrounding East Tennessee Area for over 55 years and offers honest, dependable service from certified HVAC technicians. Contact us online HERE or by phone at (865) 938-1005 to ensure your furnace or HVAC system begins blowing the correct temperate again.