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Carrier Furnace Not Staying On? 4 Common Causes (+ Fixes)

If your Carrier furnace won’t stay on, it means heating in your home is insufficient. There are several reasons for a furnace to shut off or not stay lit. This is why you need to thoroughly investigate your furnace to identify and fix the problem. 

Your Carrier furnace isn’t staying on because of a dirty crossover (between the ignitor and flame sensor), a faulty gas valve, overheating issues, or problems with the flame sensor. Ensure all parts are clean and working correctly to get your Carrier furnace to stay on.

This article will teach you to identify why your furnace isn’t staying on. I’ll also share fixes for each problem so that you can get your furnace to stay on throughout the winter season. 

Dirty Crossover Between the Ignitor and Flame Sensor

If you look inside the furnace, you should see a small part that runs between the flame sensor and ignitor. This is the crossover, and it’s responsible for sending signals between these two components in the furnace.

Many people overlook the possibility of the crossover being faulty when their Carrier furnace won’t stay on. A dirty crossover can cause problems with the signal sent between the two connected components. 

The furnace may ignite, but the flame on the burners goes out fast. Moreover, the flame sensor won’t send a new signal to the ignitor.

How To Fix

In most cases, the crossover is simply dirty. The dirt interferes with the functioning of the crossover, so the sensor and ignitor can’t communicate effectively. Here’s how to fix the problem:

  1. Turn the furnace off.
  2. Open the main compartment.
  3. Find the crossover. It’s between the ignitor and flame sensor.
  4. If it’s dirty, clean it using a small brush. Avoid touching the ignitor and any other part of the furnace.
  5. Once cleaned, close the furnace and test it.

Faulty Gas Valve

When the furnace is turned on, the gas valve opens up to allow gas to flow into the furnace. The gas is then used to create ignition inside the furnace. 

When the gas valve is faulty, it can cause some gas to pass through but then fail to open again. This means ignition was successful, and some heated air got into your home. 

However, when the second heating cycle occurs, the gas valve remains shut. No gas means no flames. The furnace may stay on, but no heat will come from the device.

How To Fix

Start by checking if something is blocking the gas valve. If it’s a partial blockage, gas may still enter the furnace, but it won’t be nowhere near enough to keep the flame on the burner going. In other instances, the gas valve itself isn’t working as it should.

This is what you have to do to fix the problem:

  1. Turn off the furnace.
  2. Open the main compartment.
  3. Disconnect the gas valve from the supply line on both ends.
  4. Use the appropriate tools to remove the gas valve.
  5. Replace the gas valve with a new, identical model.
  6. Reinstall the gas valve and connect everything back together.
  7. Test to see if it works.

Here’s a video guide showing how to replace a gas valve:

Overheating Issues

The furnace can get quite warm when it heats air to blow into your building. However, sometimes there’s too much heat. 

When this happens, the electronics in your furnace overheat, resulting in a tripped temperature limit switch. And if the switch trips, the furnace won’t operate any further. The switch prevents severe damage to your HVAC. 

There are a few reasons your furnace is overheating. A dirty air filter is the most common one. The cause may be related to the limit switch too. If the temperature limit switch is faulty, it can trip even if the furnace isn’t overheating. 

How To Fix

The first step is to determine why the furnace is overheating:

  • Start with the air filter. After turning off the furnace, remove the filter and check if it’s dirty. If you find a layer of debris, clean it properly and place it back into the furnace. 
  • If the filter isn’t dirty, check the limit switch. See if the limit switch has tripped. If so, reset the switch and try again. Get a replacement if the switch continues to trip even when the furnace isn’t overheating.

The video below will show you how to replace the switch:

Problems With the Flame Sensor

Apart from the potential causes mentioned above, the flame sensor is another piece you must check. The sensor is responsible for detecting a flame in the furnace. The sensor tells the gas valve to close if no flame is detected.

There are two possibilities here. Your flame sensor may be dirty and needs cleaning. The other possibility is that it’s broken.

How To Fix

Here’s what you have to do to fix the flame sensor:

  1. Turn off the power to the furnace.
  2. Open the main compartment and find the flame sensor. It’s attached to a metal rod in the combustion chamber.
  3. If you see a thick layer of soot, clean it.
  4. Get a replacement unit if you see cracks or other visible damage on the flame sensor.
  5. Return the flame sensor to the furnace.
  6. Test the furnace.


A faulty gas valve, dirty flame sensor, or overheating problems can cause your Carrier furnace to shut down unexpectedly. You should investigate what’s causing the problem, starting with the most common reasons. 


  • Chris Hewitt

    Chris is a Texas-based freelance writer who loves the outdoors and working in his garage. When he's not enjoying the Texas sun, he can be found tinkering with all sorts of things in his workshop.

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