Why is My Furnace Blowing Cold Air?

woman wearing winter jacket and hat inside because furnace is blowing cold air

If you furnace is blowing cold air in Massachusetts, we’re sorry! No one should have to weather (pardon the pun) 20-degree weather while your vents blow cold air.

A furnace blowing cold air is actually one of the most common furnace problems reported each winter by Framingham-area homeowners, so you’re not alone! The other piece of good news: this problem may be easy to solve and won’t cost a dime!

Below, we’ve outlined five reasons why your furnace is blowing cold air—and what you can do about them. Of course, you can always give our Framingham heating repair pros a call, too!

Call (508) 881-1500

1) It’s Normal

If the air coming out of your vents is only cold when it turns on but heats up after a few seconds, this is normal operation.

For example, when you turn on a hot water faucet, it takes a little time for the hot water to travel from the water heater to the spout. In the same way, when your furnace turns on, it must clear out the cold air already in your vents.

2) Your Thermostat is on the Wrong Fan Setting

Many Framingham-area residents turn on their heating system for the winter and then notice they are being treated to a constant flow of cool air. This isn’t necessarily a problem with your furnace – it could be your thermostat!

When your thermostat’s fan setting is set to “ON”, the fan is running at all times, whether the air is being heated or not. Set your thermostat to “AUTO” so that the fan only turns on when the furnace is running, and only heated air will come out of the vents.

3) Your Pilot Light is Out

For homeowners with older gas furnaces, a furnace that only blows cold air can be a sign that the pilot light has gone out. This causes the furnace to keep blowing air, even if the air is not being heated. Follow the steps below to re-light the pilot light and solve the problem:

Step 1: Locate pilot light assembly and switch

The assembly and switch are usually located at the bottom of the furnace near a small knob that usually has these 3 settings:

  • “Pilot”
  • “Off”
  • “On”

Your furnace’s user manual should have a diagram to showing you where it is.

Step 2: Turn the switch’s knob to “Off”

After turning the knob to “off”, wait 3-5 minutes. Make sure there’s no gas coming out of the pilot.

Step 3: Turn knob to “Pilot”

This re-starts the flow of gas to the pilot.

Step 4: Hold down reset button and hold a light at the pilot opening

Hold down the reset button on the pilot control panel and hold your lighter to the pilot opening until the flame lights. The flame should be a steady blue cone.

Step 5: Turn the knob to “On”

The furnace should ignite and should only blow hot air.

If the pilot flame won’t light or won’t stay lit, then the pilot light opening may be dirty and needs to be cleaned. It could also be that the thermocouple, a gas safety device, may be malfunctioning and needs to be replaced. Luckily, a new thermocouple is not expensive, but it will require help from a professional Framingham heating contractor.

4) The Flame Sensor is Dirty

Another common complaint is furnaces that turn on and begin heating, but then the air turns cold again very quickly. Most of the time this is a dirty flame sensor that is not allowing your furnace’s burner to remain lit.

Get a heating professional to clean the sensor. This is one of the reasons annual heating maintenance is so important.

5) It’s More Technical

Your furnace is a gas appliance with many moving parts. The reasons listed above are the most common, but there are many other things that can cause your furnace to blow cold air, such as a bad ignitor or malfunction on the circuit board.

Help from Framingham Heating Pros

If you need further help diagnosing the reason your furnace seems to be blowing cold air, reach out to us at Nicholson Plumbing, Heating & Air Conditioning today!

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  • Francis from Nicholson Plumbing and Heating was excellent. He was here to evaluate HVAC in our home. He was very patient and answered all my questions. He is also polite and easy to communicate with him. He explained technical concepts to me in layperson terms!

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  • Nicholson offered what is possibly the best customer service I have dealt with in a home repair situation.  I called them because I was looking to replace my very old furnace.  They came out to do an initial estimate, and then came back when I had some further questions about my options.  After installing the furnace, they ran into some problems with my air ducts.  This happened on a Friday, and the problem was fixed by Monday afternoon.  In addition to their excellent service, they did quality work at a fair price.  I would recommend them to anyone looking for an HVAC company in the Framingham area!

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