My tenant is angry and I want to fix this for him. It’s freezing outside, and all you want is to get in your car and turn on the heat. Otherwise your electric heater or gas furnace will not turn on. When the furnace is … If the flame sensor is dirty, it will produce inaccurate readings which can cause heating issues. First – make it worse. Unfortunately, it isn't uncommon for an HSI to malfunction. Also, if your oil burner isn't functioning correctly you should check for a clogged filter. Another cause may be that you have a faulty limit that is opening prematurely. Heating up air uses a lot of energy and is financially costly. I have a Trane XE 90 furnace. 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. Discussed here: what to check if the forced warm air furnace blows cold air out of the supply registers, or cycles between blowing warm air & cold air. If your furnace starts blowing warm but then quickly turns cold, the flame sensor may need attention. 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. Check the following two switches to make sure that the furnace blower fan is not simply set to run continuously: If you need to introduce outdoor air into a building for air quality reasons, consider an air to air heat exchange system to save on heating costs. When heat called for and fan comes on it blows cold air, then heat, then cold, then off. Check to see if one of these troubleshooting tips fixes the issue. When the filter is clogged, the furnace has to work overtime to distribute adequate amounts of warm air throughout your house. Once every few days, the furnace will kick on as normal, send out heat, but after a few minutes we’ll notice that it’s blowing cool air. We’ve replaced the flame sensor, the filter is clean. Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia. As your oil or gas-powered furnace heats the air, condensation is created. It has a clean air filter in it also. The fan blows fine. Check the air filter. The thermocouple is a sensor that regulates ignition, and if it requires adjustment or replacement your furnace will blow 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 the flame stays on, great! In fact, the problem may be as simple as changing your filter! Used to work fine and then during a repair in 2016 all the ducts were fully opened- my mistake. 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. The furnace fan limit switch assembly is intended to be adjusted within a safe range by the heating service tech by moving the stops, but if you bend something the switch is damaged and unsafe, and if you set the switch incorrectly (for example fan coming on too late or turning off too early, or setting the upper limit too high) there is risk of overheating the heat exchanger, cracking it, risking fatal carbon monoxide poisoning at worst, or perhaps a costly heat exchanger or furnace replacement job. 3) Pilot light is out If your gas furnace is only blowing cold air, then the pilot light may be out. 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. All Rights Reserved. If this is the case, you'll first want to turn the gas valve that supplies the pilot light off. To mitigate carbon monoxide and puff backs, an internal motor kicks on and creates a vacuum just before the burner engages. Again using Occam’s Razor, we can assume that the next likely culprit for your heater blowing cold air is your thermostat. There are many reasons your car's heater isn't working. This will eliminate the risk of freezing. The electronic trouble code is 8, which means the gas pressure is low I have changed the gas valve and the flame sensor … read more Any help would be appreciated. Use a wrench or pliers to remove the pilot tube. Pilotless furnaces have been an energy-saving breakthrough for the home and commercial heating industries. Your body temperature is around 98.6°F (everyone’s body temperature is slightly different, but that’s the average). Check that the air filter is clean and that the ductwork is not obstructed. After checking that your fuel level is adequate and your filter is clean, the next area to check is the flame sensor. We have owned home 12 years. Ensure that your thermostat is set higher than the temperature in your home. It blows hot air and then cold air. Changing your furnace filter is an important part of caring for your HVAC system and it should be done, at minimum, every three months. A dirty air filter blocks airflow over the furnace’s heat exchanger, causing it to overheat. You might be suprised to learn that one of the most common residential HVAC issues is the thermostat. Ductwork is often installed in areas such as attics, garages or crawl spaces where there isn't temperature control. 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. The oil from your fingers can cause permanent damage to the part. Your furnace may be blowing cold air because the filter is too dirty. Once the vacuum is created, the vacuum switch sends a signal for the furnace to ignite. 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. But still the same issue. When I turn the furnace off and then back on again from the thermostat it then blows warm air again. 2. The motor can be faulty or seizing up causing it to not spin fast enough to move enough air through the furnace. If we increase the thermostat to 70 the downstairs overheats up to 78 degrees in about 15 minutes-so we turn it down again, and then he is cold. 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. When the furnace resumes heating, I see the normal flashes of 20 green followed by one red. We live in central NY-temps during the winter are from 30 to minus 15. Check out, On 2020-12-16 If your pilot light did go out, try to relight it. It willheat for a bit but then blows cold air. Heat pumps are a different beast altogether. by (mod) - furnace blows cold air - what to check first. If we close them the heat will stay on longer and it will get too hot. It is important to note that constant overheating can damage your heat exchanger. Gas forced air furnace is Lennox G16 24 years old, in good condition. InspectAPedia tolerates no conflicts of interest. Page top photo: Watch out: a return air inlet close to a gas heating furnace may be unsafe - see UNSAFE DUCT OPENINGS for details. I don't know what's happening with your heating system but I can, from your note make a few diagnostic suggestions: Watch out: you are quite right not to force the set point adjustments on a fan limit switch. If after refilling the tank your furnace doesn't turn on, it may be necessary to manually bleed and restart your furnace. Change the air filter If your furnace overheats, it could end up blowing cold air. Although you can do this yourself, we recommend calling a professional as there may be another underlining problem. A dirty furnace filter can limit the airflow through your furnace and cause it to overheat, which will shut it off automatically. 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. This is a likely cause if your furnace blows hot air, then cold. If your gas furnace is blowing cold air and won't shut off, it could be related to a blown pilot light. Another telltale sign is if your utility bills are higher than they should be based on use. 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. If the switch is in the ON position, then the blower keeps running, even when the furnace is not heating. There's a lot of issues that can cause your ducts to leak. Two different people worked on the 2016 repair. If your furnace is blowing cold air, or is not operating at all, a component called the fan limit switch may have malfunctioned. Limit switch is at off 100, on 125 off 150. While the system is in cooling mode, the frost that had built up on your outdoor coil then turns to water, runs … When this is the case there's a good chance that the material will degrade and begin to leak. If the ducts can be directed, make sure they point away from the thermostat. Let us know what you find as that will help others. Use care not to touch an HSI when troubleshooting or installing a new one. Since the draft motor was noisy we replaced that as well. Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly. That may be a quick and easy fix. 1. Many times the problem can be resolved by restoring the thermostat to it's factory default settings. Warm air is sent through your ducts when the thermostat says it’s needed. If this doesn't resolve your cold air problem it could be the themostat itself, but before calling a professional, we recommend trying the other troubleshooting suggestions first. If you own a gas furnace, there are several potential things that can cause cold air to blow when you're expecting hot. There is one furnace in the basement and one thermostat -in the upstairs apt. The pilot light is another common culprit of gas furnace problems. Can you say what we ought to check? In a furnace, the heat being produced and blowing into your home starts out at upwards of 110 or more degrees, often much higher than that. In such cases, a safety control device known as the limit switch will shut off the burners. Pilotless ignition furnaces use a flame sensor to keep the furnace burning once it starts. More diagnostic details are at FURNACE FAN CYCLES DURING HEAT, Our 22 year old furnace just started having intermittent problems. New furnaces are equipped with a spark ignitor or electronic ignition, which may require a technician to repair. - J.C. 4/15/2013. If left, it will just keep blowing cool air. Two story 75 year old classic cape cod home. One of the most common causes of a furnace blowing cold air is not actually a repair at all. If not, then keep reading. Apologies for the delay. Your furnace may or may not be blowing cold air if your ductwork is leaking, but you may have noticed it more challenging to keep one or two rooms warm. If you have a gas furnace, a lack of fuel will cause the pilot light to go out. As a pilotless burner owner, you'll want to keep your fingers crossed that your issue isn't related to your burner's circuitry. It has always done this. Thanks for the interesting question and the excellent photo. Should we try more duct adjustments or is this something else? An HSI or Hot Surface Ignitor is the most popular way to ignite a pilotless furnace. But in some buildings where heating ducts run through cold spaces and are not well insulated, or in installations in which the heating system is inducing cold outdoor air into the duct system, when the furnace burners are off the system will indeed blow cold air onto building occupants. When heat called for and fan comes on it blows cold air, then heat, then cold, then off. If the flame sensor is dirty, it will produce inaccurate readings which can cause heating issues. Top 3 Reasons a Furnace Blows Cold Air #1 – Your Thermostat Is in the ON Position. 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