Why Does Your Furnace Ignite And Then Turn Off?

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Most people like problems that seem clean and simple. If your furnace isn't heating your home, the simple answer is that it's not igniting. However, real-life HVAC problems can often be much less straightforward. One common issue that can perplex many homeowners is a furnace that briefly turns on, ignites, and then shuts off again. 

This problem can be frustrating because you may hear or see your burners igniting. You may even feel a brief blast of warmth from your vents. Despite this, the furnace quickly shuts down again, leaving you shivering in your home. What's happening, what can you do about it, and how serious is the problem? Keep reading to find out!

Why Furnaces Shut Down

Once your furnace ignites, there are two potential reasons that it may shut down again:

Assuming your thermostats are functioning correctly, the latter case will only occur once your furnace operates for long enough to reach your setpoint. Your furnace can't heat your home if it shuts down almost immediately, so it's typically the former case that leads to rapid short cycling. Several safety features can stop your furnace from igniting, but only a few will shut it down once it does.

How Safety Features Can Leave You Cold

The most common cause for a quick shutdown is the flame sensor. This sensor detects ignition and cuts the gas supply if your furnace fails to ignite, preventing potential gas leaks. If the sensor is faulty, it may fail to detect successful ignition. As a result, the sensor will cut off the gas supply, causing your furnace to go off almost as quickly as it can start.

The other potential issues are the over-limit switch, which detects excessively high temperatures, and the flame roll-out switches. The over-limit switch usually won't trigger immediately, but the roll-out switches might. These sensors detect the presence of a dangerous condition known as flame roll-out and will trigger an immediate shutdown once they detect it.

What You Should Do

Unfortunately, the reasons for your furnace to shut down quickly can range from relatively minor (a dirty or faulty flame sensor) to severe (flame roll-out). Because of the potential dangers involved, it's critical never to bypass a safety switch that's stopping your furnace from operating. Instead, contact an HVAC professional to diagnose the issue.

A professional will help ensure that your furnace isn't suffering from a dangerous issue, and they'll also have the tools and experience to test each component and find the specific fault. This thorough diagnosis ensures that you can solve the problem on the first try without throwing money at parts that may still be working fine.

Reach out to a service such as Myers Heating & Cooling to learn more.