Heating
Furnace Repair in Colorado Springs, CO

Having your furnace start blowing cold air can be incredibly frustrating. A malfunctioning furnace is obviously a serious issue since it can result in your home quickly becoming uncomfortably cold. That’s why you want to make sure you know what things to check for if your furnace blows cold air, as it may be something you can easily resolve on your own. In this article, we’ll look at the most common causes of this issue and how to know if it’s something you need to have a professional fix.

Incorrect Thermostat Setting

Whenever you notice cold air coming out of your vents when your heating should be on, the first thing to do is check the fan setting on your thermostat. You always want to leave the fan set to “Auto” so that the furnace blower only runs and circulates air when the furnace itself is on. If you have the fan instead set to “On,” the blower will run constantly. That means it will quickly start blowing cool air throughout the house soon after the furnace shuts off, and it will continue doing so until the thermostat signals the furnace to turn back on.

Malfunctioning Thermostat

Another possibility is that your thermostat is malfunctioning and has signaled the blower to turn on but not the furnace. As with most other things on this list, that issue is something you’ll need to have a professional technician check out. The technician will be able to quickly test the thermostat and determine if it or something else is the culprit. If they determine your thermostat is bad, you’ll need to replace it. In this case, it’s definitely worth switching to a smart thermostat since it can help you save money on both your heating and cooling bills.

Pilot Light Is Out

If you have an older furnace with a pilot light, another thing to check is that the pilot is still lit since the burners can’t ignite if it’s out. A pilot light can sometimes get blown out by a draft or go out because of an issue with its thermocouple.

Relighting a pilot light is fairly simple, but you first need to shut it off and wait around 30 seconds before trying to light it. You then need to turn the pilot knob to “On” and press it in with one hand while simultaneously pressing the igniter button with the other. Once you can see the flame, you need to continue holding the knob in for 30 seconds. If it won’t light or doesn’t stay lit when you release the knob, you’ll need to have a technician check it out. In most cases, this issue indicates that either the pilot gas tube is clogged or that the thermocouple is worn out, dirty, or bent.

Dirty or Worn-Out Flame Sensor

The flame sensor is one of several safety mechanisms in a modern furnace, and its purpose is to prevent gas from flowing to the burners if they suddenly go out or fail to light. Flame sensors sometimes only last for around five years before they start wearing out and malfunctioning occasionally. If the sensor does malfunction, it can lead to the gas valve closing and the burners suddenly going out partway through a heating cycle. The same can happen if the sensor is overly dirty since it may sometimes suddenly stop detecting the burners, which is why you should always have a technician clean the sensor yearly. If there’s an issue with the flame sensor and the burners go out before the heating cycle finishes, the blower may continue to run for a few minutes and start blowing cold air.

Furnace Overheated

One of the most common reasons a furnace system will blow cold air is due to the furnace overheating and shutting off. There’s another safety mechanism inside a modern furnace known as the temperature limit switch. This switch is specifically designed to shut the furnace off in case it overheats so that the extreme heat doesn’t damage any components or potentially lead to the furnace catching on fire. It is also tied to the blower and is basically what tells the blower when to turn on and off.

The way the limit switch works is by sensing the temperature of the furnace’s heat exchanger. Once the exchanger heats up to a set temperature, the switch sends a signal to the control board telling it to switch the blower on. If the switch senses the heat exchanger is above a certain temperature, it will then signal the control board to close the gas valve and turn the furnace off. However, the blower will continue running for at least five to 10 minutes so that cool air continually flows over the heat exchanger to cool it down more quickly. In some cases, the blower could even run for up to 30 minutes and continually pump cold air out of your vents until the furnace finally cools down and the blower shuts off.

Limit Switch Issue

Once a furnace finishes a heating cycle and its burners shut off, the blower will continue to run for a few minutes. This is partly so that the remaining heat in the heat exchanger isn’t wasted and, as mentioned earlier, to help the exchanger cool down to a safe temperature. In some cases, the low range of the limit switch can malfunction, meaning the switch fails to register that the heat exchanger has cooled down. When this happens, it can lead to the blower just continuing to run and blow cold air. If the blower fails to shut off, it can also sometimes result in the furnace not being able to turn on again when it should.

If you notice that the blower runs continuously for more than 15 to 20 minutes when it is set to “Auto,” one thing to try is turning off the circuit breaker for your HVAC system. This will cut the power to the blower so that it immediately shuts off. Once you flip the breaker back on, there’s a chance the issue will be resolved and your furnace will again work as it should. However, you’ll need to call for professional furnace repair if the issue happens again.

Malfunctioning Control Board

The last possibility is that the furnace’s control board is faulty or malfunctioning. It could be that it’s either not receiving the signal from the temperature limit switch to turn the blower off or that it isn’t sending a signal to the blower. In either case, the result is that the blower will just keep running and quickly start circulating cold air. This is another situation where just switching the circuit breaker off and then back on could resolve the problem. However, if the control board is faulty, the issue will usually happen again and again until you have the board replaced.

Since 2015, Alphalete Plumbing Drain Heating & Air has been providing quality HVAC, plumbing, sewer, and excavation services throughout the Colorado Springs area. Our experienced technicians work with all brands and models of HVAC equipment and can help if your furnace is blowing cold air or you have any other problems with your HVAC system with a repair or a brand new furnace installation. To schedule an inspection and get to the bottom of your furnace issues, contact us today.

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