6 Reasons Your Pilot Light Lit But Burners Won't Ignite

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Pilot lights and burners are crucial parts of water heaters and furnaces. Water heaters allow you to enjoy showering or using water, especially during the cold season. Furnaces enhance the look of a room, making it beautiful and cozy. It also helps make the space warm to stay in, especially during the cold season. But then, when either of them stops working, you’ll be worried and look for ways to solve the problem.

One of the issues you can encounter with your furnace/water heater is when Pilot Light Lit But Burners Won’t Ignite. This can be a problem with the control valve, and it can be that the thermopile can’t sense the flame or the burner line is rusty. Other possible reasons are a damaged thermocouple or faulty auto-shut-off or if the furnace vent is closed.

These are things you can easily fix after identifying the root cause. But do you know how? Read on this article to get an in-depth explanation of all this.

Table of Contents

Why Pilot Light Lit but Burners Won’t Ignite?

Is The Thermocouple Rust-Covered?

One of the reasons your furnace burner won’t ignite while its pilot light lights are because of rust on the thermocouple. If the thermocouple is rust-corroded, the unit will also not work normally. Remember thermocouple measures the temperature, and if it is not operational, the water’s temperature won’t be as you’d wish. This will make the burner not to be functional too.

You can stop this problem by removing the rust on the thermocouple. This is simple as you only need to clean then vacuum the thermocouple. But first, switch off the gas valve to pilot and dismantle the cover plate, then check if it’s rusty.

If you want to clean it with ease, go for a vacuum cleaner with a brush attachment. This will help you wash away all the dirt and debris on the thermocouple. Do this carefully not to break the pilot light or gas fitting.

But if you realize that after washing the thermocouple isn’t in perfect shape, consider replacing it. But if it doesn’t still work after replacing it, then that’s not the problem. So, check if the connection between the sensor and the pilot flame is well. It could be that it accidentally came out, so it can’t sense enough heat preventing the gas control valve on the main burner from opening. You can replace your thermocouple if it doesn’t work after trying either of the solutions.

It Could Be an Issue with The Burner Line

Sometimes the problem could be on the burner line, making it not ignite. This can be because of a corroded burner line or leakage, which interferes with how it works. But if the burner line and jet are also full of dirt or debris, it will experience this problem.

To fix this, remove the burner and check if the lines or jet are okay. If they’re dirty or rusty, use an air compressor to blow them out. But if there’s a leakage and you can smell gas, turn off the gas line, go sit outside and call your technician.

Thermopile Is Unable to Sense the Flame

If your pilot light is lighting well, but the burner won’t ignite, then chances that the thermopile cannot sense the flame are high. This could be because it’s dirty or corroded, interfering with normal operation.

It’s advisable to measure the output of the thermopile using a multimeter before you clean the rust. If the output is around 350mV, it’s fine. But if it’s less than that, remove it from the burner, clean the dirt and rust, and check if your burner can ignite again.

The Control Valve Has Issues

Another reason that can make the burner not ignite while the pilot light is functional is a faulty control valve. This will be because the electronics in the valve won’t sense when the pilot light is lit. When this is the problem, you need to have enough money to replace the whole assembly as it’s something you can’t fix.

Note that the valve could also be faulty because of a problem with the control knob. If the control knob gives you a hard time using it, don’t force it to work. Instead, change the valve. But the issue could also be when the high limit powers off the valve. When this happens, the high limit won’t reset itself until the thermostat malfunctions making the water reach extreme temperature. The only solution still is replacing the valve.

When replacing the control valve, ensure you are safe as the gas can be harmful to your health. If you don’t know how to replace the valve, don’t hesitate to call your technician to help you out. But it’s advisable to check if the valve has a leakage before reinstalling them.

There Could Be a Problem with The Auto-Shut Off Button

Your furnace burner may also fail to ignite when there’s an issue with the automatic shut-off button. This means that when the burner goes off, the pilot light doesn’t shut off, making it light while the other fails to ignite.

This you can solve by gently tapping the control valve using a screwdriver. Doing this will help you put off the pilot light after removing the small disk. But if you’re unable to get the small disk, switch off the control knob. After that, switch off the dial of the control knob to put off the pilot light. Then remove the thermocouple out of the unit and replace it with a new one to solve the problem.

Is The Automatic Vent Closed?

If your burner won’t ignite, it’s because the vent is closed. Remember, burners have two switches for flame rollout and flue gas spill switch. If any of them has issues, your burner will also fail to ignite. You, in this case, need to open the automatic vents to enable the burner to ignite. But don’t fail to check if any of the two switches are operational. If you find any has a problem its best to replace them.

FAQs About Pilot Light Lit But Burners Won’t Ignite

Is pilot light found in all the gas furnaces?

No. Pilot light is only found on the older models where it helps to ignite the burner. However, the newer versions of gas furnaces use an electric ignition system to ignite the burners.

Will dirty burners prevent them from turning on?

Yes. If your burners are full of grim, they won’t be able to draw enough oxygen that will enable it to ignite. But you can clean them with the help of professionals and have them functional as before.

What if the flame sensors have a problem?

If your furnace flame sensor has issues, the burners will not work as they should. This is because it will switch it off to void unburnt gas buildup if the pilot light isn’t working. So, the burners will become faulty.

Bottom Line

If your pilot light is lit, but the burners won’t ignite, the problem could be on the burner line or thermopile. This could also be because of a faulty gas control valve, corroded thermocouple, or a closed vent. Some of these issues you can easily fix without the intervention of a professional. However, if you’re not sure of what to don’t hesitate to call your technician to help you diagnose the problem. If you’re to replace any part, do so, but dirt and blockage will require you to clean the parts and have your burners operational as usual.

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