If you only feel your furnace blowing cold air briefly, and the air is quickly replaced by warm air, this is the most likely explanation. Pilotless furnaces have been an energy-saving breakthrough for the home and commercial heating industries. If you own a gas furnace, there are several potential things that can cause cold air to blow when you're expecting hot. With that said, even if you recently changed your filter you should check it again. InspectAPedia tolerates no conflicts of interest. Limit switch is at off 100, on 125 off 150. But before you call for help, you might be able to do some simple troubleshooting and save yourself a little money by fixing it yourself. - J.C. 4/15/2013. If you have a gas furnace, a lack of fuel will cause the pilot light to go out. If the flame sensor is dirty, it will produce inaccurate readings which can cause heating issues. Changing the dirty air filter can solve this problem. Help, we have an up/down duplex with forced air natural gas, installed in 2010. We’ve replaced the flame sensor, the filter is clean. Use a wrench or pliers to remove the pilot tube. Ensure that your thermostat is set higher than the temperature in your home. it resets and works properly. If the vacuum does not occur, the furnace will not ignite. I like Dan Holohan's expression "Keep your hands in your pockets" - my mom used to make me sitOn my own hands. Leaky ductwork can cause serious issues for your heating system. But you might want to consider calling a professional HVAC service who has the knowledge, tools and experience to find and repair the problem. Change the air filter If your furnace overheats, it could end up blowing cold air. Such leaks not only increase heating costs unnecessarily, they also are unsafe. Although you can do this yourself, we recommend calling a professional as there may be another underlining problem. Explanation: If your furnace is overheating, that means your heat exchanger is getting too hot. If you're lucky, the problem may be as simple as changing a fuse on the circuit board. As I said all was working well before the repairs as far as I know (maybe other tenants just didn't complain to me?). You can easily fix this problem by thawing the condensate, but you'll need to take long term measures to prevent the issue from happening again. When the furnace resumes heating, I see the normal flashes of 20 green followed by one red. Would it matter if the return/supply "loop" for each apt were separate somehow? Since the draft motor was noisy we replaced that as well. Or maybe the air starts off hot, then turns cool before the furnace shuts down. Possible Conclusion 1: It’s Not Blowing Cold Air. Note: appearance of your Comment below may be delayed: if your comment contains an image, web link, or text that looks to the software as if it might be a web link, your posting will appear after it has been approved by a moderator. If you find that you go to bed comfortable and wake up freezing because instead of your heater delivering warm air, it's blowing cold, it might be because the condensate drain has frozen. New furnaces are equipped with a spark ignitor or electronic ignition, which may require a technician to repair. This can be a little bit confusing, so let’s clarify it carefully. If this doesn’t fix your problem, and your furnace is still not blowing hot air, you can move on to some of the other potential culprits. This will eliminate the risk of freezing. We have owned home 12 years. But if it doesn't light, or it won't stay lit, you'll want to check that gas is flowing to the pilot. It has always done this. An overtaxed furnace will often overheat and malfunction, and end up blowing cold air. Your furnace may be blowing cold air because the filter is too dirty. You may also see an error message on your thermostat, or a blinking LED light on the furnace control board. What do you think? However, the fan will keep running, cooling the furnace to protect it from potential damage. First – make it worse. Unfortunately, it isn't uncommon for an HSI to malfunction. The condensation must be removed from the system and if your condensate drain terminates outside your home, it can freeze. If the switch is in the ON position, then the blower keeps running, even when the furnace is not heating. One of the most common causes of a furnace blowing cold air is not actually a repair at all. The dirty air filter blocks the airflow, causing the furnace to run longer to heat your home until it overheats. It’s Just Been Switched On – Any furnace will blow cold air when it starts up, since it takes time for hot air to travel through the system and into your home. Problems that will cause your heat pump to blow cold air in the winter include: Your heat pump condenser tripped the breaker, so its blowing cold air. Have an expert inspect your ducts along with the furnace. When the fan is on, the furnace will continue to blow, regardless of whether or not the air is being heated. Changing set points on limit switch does not seem to change pattern. Upon dissection of draft motor is was covered with white crusty minerals probably from the water from the humidifier mounted on the nearby cold air return. Unfortunately the photo you sent had a virus - we had to clean it up so what we display here is a bit different and at at lower resolution that your version. According to the book the 2 red flashes means "Retries or recycles exceeded". It blows hot air and then cold air. It seems to me if we open the ducts more fully to the thermostat area then heat will shut off sooner, and downstairs will be even colder.. Your thermostat has an ON and AUTO switch that runs your blower. But according to downstairs tenant the fan is not on. 2. Inadequate gas supply. Maybe the fan is malfunctioning. If you own an electric furnace and it's blowing cold air there's a few things that could be causing the problem. Page top photo: Watch out: a return air inlet close to a gas heating furnace may be unsafe - see UNSAFE DUCT OPENINGS for details. Check for an air duct leak, particularly, leaks from cold areas such as an un-heated crawl space or basement into the return air duct system. Your furnace blowing cold air could be caused by hot air escaping through holes in the duct work that carries the heat throughout your building. Let’s look at some of the solutions to this common furnace problem. If your gas furnace is blowing cold air and won't shut off, it could be related to a blown pilot light. Changing your furnace filter is an important part of caring for your HVAC system and it should be done, at minimum, every three months. The major issue that can cause this problem is a heat exchanger issue. We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need. If the flame sensor is dirty, your furnace will turn on and begin heating but then turn cold … As soon as the furnace cycles back on the air will warm up again. Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia. Help! There is one furnace in the basement and one thermostat -in the upstairs apt. Keep us posted - what you learn will help other readers diagnosing a fan limit switch problem with their own furnace. I have an electric furnace that blow cold air sometimes. Check to see if one of these troubleshooting tips fixes the issue. More diagnostic details are at FURNACE FAN CYCLES DURING HEAT, Our 22 year old furnace just started having intermittent problems. Either hot air from the duct is blowing on the thermostat, causing it to think the RV is warmer than it actually is, or cold air is blowing across the thermostat, resulting in a similar issue. If the ducts can be directed, make sure they point away from the thermostat. When this is the case there's a good chance that the material will degrade and begin to leak. Should we try more duct adjustments or is this something else? Check that the air filter is clean and that the ductwork is not obstructed. A dirty air filter blocks airflow over the furnace’s heat exchanger, causing it to overheat. But if you’ve set your fan to be “on” at all times, it’ll blow cold air during the furnace downtime. So why does the downstairs get so cold when thermostat is 68 and way way too hot at 70? If we close them the heat will stay on longer and it will get too hot. If you notice your furnace only blows cold air on occasion but your home is still maintaining its temperature than this may be simply a setting on your thermostat. When heat called for and fan comes on it blows cold air, then heat, then cold, then off. Can you say what we ought to check? One safety bypass he made was found during the repair and corrected. Am I missing something here? If you choose to call a professional to do the job for you, this would be a good time to have your system inspected. The reason the fan shuts off during this process is so the system doesn't pull the cold air from the outside across the coil while the hot refrigerant circulates. The fan blows fine. Now about that pesky fan limit control, you could. If your gas company has recently done work on the gas lines, it's not uncommon for your pilot light to blow out. It has a clean air filter in it also. If the flame sensor is dirty, it will produce inaccurate readings which can cause heating issues. These Common Issues May be the Reason, AC Evaporator Coils: Everything You Need to Know, AC Compressor Not Working but Fan is Running, Evaporator Coil Leak: What You Need to Do, Looking for A Portable Air Conditioner That Doesn’t Need A Window, Why Your Furnace is Short Cycling and What to Do About It, Best 50 Gallon Electric Water Heaters: Our Top Picks. After checking that your fuel level is adequate and your filter is clean, the next area to check is the flame sensor. If your ducts have cracks or worse, then the cold air blowing into your house might be coming straight from outside right into your ducts, mixed in with the warm air your perfectly functional furnace is producing. Warm air is sent through your ducts when the thermostat says it’s needed. Once the vacuum is created, the vacuum switch sends a signal for the furnace to ignite. To mitigate carbon monoxide and puff backs, an internal motor kicks on and creates a vacuum just before the burner engages. When the condensate drain freezes, it causes condensation to drip back into your system and trigger a shutdown. The Flame Sensor is Dirty. While the system is in cooling mode, the frost that had built up on your outdoor coil then turns to water, runs … There's a lot of issues that can cause your ducts to leak. Continue reading at FAN LIMIT SWITCH TROUBLESHOOTING or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX. Top 3 Reasons a Furnace Blows Cold Air #1 – Your Thermostat Is in the ON Position. Copyright 2021 Think Tank Home. You start it up and hit the heater. If the flame stays on, great! 3) Pilot light is out If your gas furnace is only blowing cold air, then the pilot light may be out. It's blowing warm air at the moment. Your furnace blows hot air but that air quickly turns cold then the furnace shuts off altogether. In some buildings we like to run the blower fan continuously for more even heat distribution and improved air filtration - improvements to building indoor air quality. In addition, there are a few problems that are unique to pilotless furnaces which you'll want to look into if the troubleshooting tips above don't fix your problem. My tenant is angry and I want to fix this for him. If this is the case, someone walking by the burner could generate enough of a draft to cause the pilot to go out. The thermocouple is a sensor that regulates ignition, and if it requires adjustment or replacement your furnace will blow cold air. Or the gas line isn’t supplying enough gas to your furnace. If not, then keep reading. By switching the thermostat to “auto,” the fan will only blow when the furnace is heating the air. This can be caused by something as simple as a strong draft. There are many reasons your car's heater isn't working. When a heating cycle begins and your air handler turns on, that cool air will blow out of your registers before warm air does. This is especially common if you have an older fuel tank with a less-than-accurate fuel gauge. When heat called for and fan comes on it blows cold air, then heat, then cold, then off. But still the same issue. Cold air trapped inside will need to be expelled before the hot air can take its place! A dirty furnace filter can limit the airflow through your furnace and cause it to overheat, which will shut it off automatically. I have a Trane XE 90 furnace. When overheating, your furnace can trip a high limit switch , causing the furnace burners to shut off so that the heat exchanger does not crack. Excessive heat or exposure to water can damage the circuit board, which can cause your furnace to lose some or all of its functionality. Again using Occam’s Razor, we can assume that the next likely culprit for your heater blowing cold air is your thermostat. Many times the problem can be resolved by restoring the thermostat to it's factory default settings. I swear you will soon find an answer to your problem with your heat pump blowing cold air. If your fan only runs when your furnace is heating the air, then you’re much less likely to experience your furnace blowing cold air. If your furnace is blowing cold air, or is not operating at all, a component called the fan limit switch may have malfunctioned. Perhaps your temperature gauge is … Since then the downstairs apartment gets cold (like 62-64) with the thermostat set to 68. In such cases, a safety control device known as the limit switch will shut off the burners. It willheat for a bit but then blows cold air. So 85-92°F feels cold to new heat pump owners. Heat pump systems operate pretty differently than standard furnace systems. Your furnace clicks on and the blower motor is running, but the air coming from the vents is cold or cool instead of hot. This “hot then cold air” sequence happens over and over and your home isn’t warming up. What Can I Do If My Heater Is Blowing Cold Air? Changing set points on limit switch does not seem to change pattern. If this is the case, you can simply switch the setting from "on" to "auto" and your problem should be fixed. Depending on the type of burner you have, it isn't uncommon to experience any of the issues listed above. Consult your users manual for directions on restoring the settings for your specific unit. At my request a few days ago the tenant with thermostat set the fan to be ON all the time -and assures me it's still on. You’ve got three basic options. Thanks for the interesting question and the excellent photo. If your ducts are leaking (and ENERGY STAR says that almost all homes leak about 30% of the air in their ducts), cold outside air is making its way into your ductwork. 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