How to Fix a Furnace That Won't Start

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Things You'll Need

  • Screwdriver

  • Flashlight

  • Medium grain sandpaper

Fix a furnace that won't start.

The cold weather is just around the corner and BAM! The furnace won't start. With freezing temps, your furnace is the most important appliance in your home. You absolutely cannot live without a furnace in cold weather. It's even more frustrating because you can hear the furnace clicking on and getting ready to blow the lovely warm air...but then the thing just shuts down. Here's one way to fix a furnace that won't start before you call the repair man, or woman.


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Step 1

Before you attempt to fix a furnace that won't start, make sure you know what kind of furnace you have. This ehow is strictly for a forced air, gas furnace. Check to make sure the furnace filter is clean. If not, replace the dirty filter with a clean filter. Also, check to make sure power to the furnace is on. Finally, make sure the gas supply to the furnace is open.

Step 2

If your furnace clicks on or initiates the start cycle, but does not fire up, you likely have a faulty or dirty ignitor/sensor. This is one of the most common furnace problems. Under normal conditions, the furnace is notified by the thermostat to click on, the ignitor gets red hot and then initiates the entire process of igniting the gas and blowing the hot air. Check the error codes in your furnace user manual to make sure you do not have a more serious problem.


Step 3

To fix the furnace that won't start, turn off the power to the furnace-and turn off the gas. Remove the front panel and look for the ignitor/sensor. Refer to your user manual to locate the ignitor. It is usually located near where the flames shoot out of the burners.

Step 4

Furnace sensor

Basically, the furnace will not continue in the starting sequence because the sensor/ignitor is dirty and needs to be cleaned. It is very easy to remove the sensor with a screw driver. Clean the probe on the senor by rubbing it with some medium grain sand paper. Do a thorough job, but be careful not to break the thing. Replace the sensor exactly the way you found it. Put the front panel back on, turn on the gas, and then turn on the power. Turn up the temperature on your thermostat to see if you furnace will fire up. If this doesn't solve the problem, time to call Mr. Fix-it.