Why is my flame sensor not staying lit?

Author: Dr. Sterling Cronin  |  Last update: Sunday, July 6, 2025

Dirty flame sensor If this sensor is dirty, the dirt can cause the sensor to operate intermittently. When this happens, your furnace will most likely light, but because the sensor can't properly detect if a flame is present. The sensor may signal the ignition cycle to end, which your furnace won't stay lit.

Why does my flame sensor keep going out?

Do flame sensors wear out? Flame sensors wear over time. However, often the problem is a dirty sensor, rather than a broken one. Since these sensors are designed to have a low tolerance for reading variations, they might misread from the slightest carbon coating.

Why wont my furnace stay lit after cleaning flame sensor?

If the flame sensor is clean but the burners still shut off around 6 seconds after ignition, this may be the result of a faulty ignition control. A common cause of a faulty ignition control which fails to sense flame is water damage.

Why are my burners not staying lit?

There are many possible reasons why the burner will not stay lit - the gas jet may be blocked, the valve may be set too low, the air flow may be restricted, there may be an issue with the pilot light, and so on.

Why does my furnace flame only stay lit for a few seconds?

Are your furnace burners only coming on for a few seconds? This is the most common furnace problem which also happens to be the easiest thing to fix! Every furnace is different but almost all of them have a flame sensor. If your flame sensor is dirty or covered in a layer of dust, it will shut the burners off after lig.

Furnace Burners Dont Stay On! SOLVED

How to know if a flame sensor is bad?

Top 7 Signs of a Bad Furnace Flame Sensor
  1. Flue Line Corrosion. The flue line is responsible for venting harmful gases from the furnace outdoors so nothing seeps into the house. ...
  2. High Energy Bills. ...
  3. Yellow Flames. ...
  4. Furnace Short Cycling. ...
  5. Dirt on the Sensor. ...
  6. Visible Damage on the Flame Sensor. ...
  7. Age.

Why does my flame keep going out?

Any issues with the gas valve that supplies that gas to the flame, whether it be dirty or malfunctioning, can result in that flame going out. It's also possible that your gas supply has run low or out entirely, which will also cause the flame to blow out.

Why is my furnace igniting but not staying on?

Faulty flame sensor

This is a common cause of burners that won't stay on. The flame sensor is a safety precaution in a gas furnace that tests that the gas coming from the burners has ignited.

Why does my burner keep going out?

While the most common causes of log burners going out are insufficient oxygen, fuel or heat, stoves also rely on a properly functioning chimney. The purpose of this is to draw out exhaust fumes that could suffocate your fire.

Why wont my furnace pilot stay lit?

It may be that it's dirty and needs cleaning. It can easily be cleaned off with fine grain sandpaper. A dirty pilot tube can also prevent the pilot from staying lit. If the pilot tube is dirty, let the furnace cool down and turn off the gas.

How to reset furnace flame sensor?

There is a work-around to waiting. If there is no safety risk (like a gas leak), a furnace can be reset to bypass this wait. Turn off the furnace's power switch and wait 10 seconds before turning it back on.

What is the life expectancy of a furnace flame sensor?

While most furnaces last for 10 to 20 years, flame sensors have a much shorter lifespan of about five years. Usually, when a flame sensor goes bad, the best route is to replace it outright.

Can a flame sensor work intermittently?

Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism.

How often does a flame sensor need to be cleaned?

If it's still not operating properly, you should call for furnace repair. How Often does it need cleaned? Most experts recommend cleaning the flame sensor once a year.

Why does my fire pilot light keep going out?

If your gas fireplace pilot light keeps going out, you may have a problem with faulty pilot controls. The pilot control failing due to age or a mechanical issue can cause your pilot light to keep going out and prevent it from being relit.

How much does a new flame sensor cost?

Most furnace flame sensors cost less than $20, but if you opt to have a professional HVAC technician make the repair, you can expect to pay between $75 and $250. Need help replacing your flame sensor?

Why won't my burner stay lit?

If your burner lights for a short time but then goes out, you may have a blockage in the gas valve. The gas line is what provides fuel to the burner to keep it lit. A complete blockage often prevents the burner from lighting at all.

Why does my fire not stay lit?

The most like culprits are likely tied to some kind of problem with your setup. Anything from issues with your pilot light, clogged ports on burners, damage to heating components, and thermocouple/thermopile malfunctions can be to blame.

Why does my furnace burner keep going on and off?

A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.

Why wont my pilot light stay lit when I release the knob?

The flame will go out if you release the knob before it is hot. The thermocouple can become dirty and caked with grit, preventing it from heating up and detecting that the pilot is lit. As a result, the pilot will always go out after you release the reset button.

What causes a flame sensor to go out?

A furnace flame sensor can fail due to several reasons, including: Dirt buildup that prevents it from detecting the flame. Corrosion from moisture or improper maintenance. Incorrect positioning within the furnace.

Why is my furnace igniting but not staying lit?

Dirty flame sensor

If this sensor is dirty, the dirt can cause the sensor to operate intermittently. When this happens, your furnace will most likely light, but because the sensor can't properly detect if a flame is present. The sensor may signal the ignition cycle to end, which your furnace won't stay lit.

Why is my gas flame not staying on?

The most common cause of this is dirty or blocked burners, which is the part that you can easily take off to clean.

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