Why Is My Furnace Blowing Out Cold Air? | 3 Common Causes and Fixes

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Is your furnace being counterproductive? Cold air coming out of your furnace is a common issue that you can fix on your own once you are able to identify the cause.

One of these causes can arise if your thermostat fan is not set on auto. If the fan on the thermostat is on all the time, the furnace will continue to blow out air even when the air is not being heated. When you turn the fan to auto, it will automatically turn on when you set your thermostat and then automatically turn off when your house reaches the temperature you have set.

Another probable cause to cold air being exerted from your furnace is due to it being overheated. This can be the case if your furnace is blowing a mixture of hot and cold air. As a safety precaution, the limit switch will kick in and turn off the furnace burners when this happens. If your air filters haven’t been changed in a while, they could be dirty and causing the air flow from your furnace to be blocked. As a result, your furnace will have to run for longer to heat the air until eventually it becomes overheated. To fix this, you will need to replace your old air filters, and then see if your furnace starts only blowing out warm air. It’s important you fix this issue sooner rather than later, because repeatedly overheating your furnace will damage your heat exchanger.

If only cold air is being blown out from your furnace, then your pilot light is probably out. If you are unfamiliar or uncomfortable with trying any of these tests and procedures, then you should call a service professional. First check to make sure your pilot light is indeed out; if it is follow these next steps:

  • Try relighting your furnace pilot light. If you cannot get it to light, this means your gas is not being supplied to the furnace. To fix this, check to make sure the furnace’s gas valve switch is turned on.
  • If the gas valve switch is turned on, but is not running, make sure the pilot light is not dirty.
  • If you find that the pilot light is dirty, clean it so that the gas can begin to supply itself again.
  • Once you get it up and running again, you may find that the pilot light won’t stay lit, which means there is an issue with your thermocouple. The thermocouple will either need to be adjusted or replaced.
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