What causes a furnace to light then go out?

Another reason why a furnace ignites then turns off could be related to the flame sensor. This key component senses when the flame is on. Often, dust or dirt covers the sensor. If this happens, the sensor won’t detect the flame, and the result is the furnace shuts down.

Why does my furnace not ignite sometimes?

The pilot light or ignition sensor is usually the most common issue when your furnace will not ignite. Then, remove the front panel to find the ignitor or ignition sensor. This is typically located near the burners. If the sensor or ignitor is dirty, it will need to be cleaned.

How do you know if flame sensor is bad?

Signs of a bad flame sensor

1. Furnace burners turn on but go out after a few seconds.
2. Soot and other debris is covering the end of the sensor (cleaning the flame sensor may fix this issue rather than a flame sensor replacement)
3. Tip of flame sensor is black.
4. Porcelain/sensor casing is cracked.

How can you tell if a flame sensor is bad?

Signs of a bad furnace flame sensor are:

1. The furnace lights but then shuts down after a few seconds (short cycles)
2. The porcelain on the flame sensor is cracked.
3. The flame sensor is sooty or corroded.

How do I know if my furnace spark ignitor is bad?

4 Signs of a Faulty Furnace Ignitor

1. The Furnace Stops Running. When a furnace won’t run at all, check for a bad ignitor.
2. Your Furnace Blows Chilly Air. Unless you’ve set your thermostat to COOL, your furnace should not blow cold air.
3. Does Your Furnace Short Cycle?
4. A No Glow Ignitor.
5. We Can Replace Your Furnace Ignitor.

How do you know if your furnace ignitor is bad?

Your furnace won’t run: The most obvious sign that your ignitor is bad is that it won’t ignite, and this generally manifests itself in your furnace failing to run when you activate it.

What happens when flame sensor goes bad?

What happens when a flame sensor goes bad? If your flame sensor is dirty or faulty, it will automatically shut down the heating unit if it doesn’t detect a flame. Most furnaces will go into a safety ignition lockout when a shutdown happens three times.

Where is the flame sensor on a gas furnace?

burner assembly
WHAT IS A FURNACE FLAME SENSOR? A furnace flame sensor is a very basic part of your furnace. It’s located on the burner assembly and is just a thin metallic rod. It’s usually bent, and it sits just in front of the pilot flame inside the furnace.

Why does my furnace turn on then turn off after a few minutes?

A defective pressure switch is another key reason why your furnace turns on then off after a few minutes. The pressure switch should close with airflow from the draft inducer motor through the burner to indicate that ignition is safe. If the switch is defective, it does not notify the ignition that it is safe to continue.

What happens if the pressure switch is not working on a furnace?

If the pressure switch isn’t working, it might not close when the proper airflow is present, causing the ignition process to stall. If the ignition process stalls, the furnace will shut off. To determine if the pressure switch is defective, use a multimeter to test the switch for continuity.

What happens when a furnace fails to ignite?

If one fails, it halts the whole chain of those that come after. There are also many safety features in a furnace that help keep it safe for your family. If the furnace is experiencing problems that could result in a fire, it may fail to ignite properly. Keep this in mind when the frustration hits.

What happens if the flame sensor does not work on a furnace?

If the flame sensor is defective, it might fail to detect a flame. If the flame sensor does not detect a flame, the control board will shut off voltage to the gas valve to prevent the furnace from heating. Sometimes, if the flame sensor is dirty, it will fail to detect a flame.