The pilot light lit but burners won’t ignite! If this is the issue with your furnace, we bet you have an older model water heater. New models don’t include a pilot to ignite the heater or furnace.
So, you post on different forums and Reddit related to HVAC to solve your problem. But everyone suggests you hire an HVAC tech to fix the issue. Yes, we agree with them but hiring an HVAC expert will cost you a lot of bucks. You can save money if you can troubleshoot the problems.
Fortunately, we are here to take responsibility and troubleshoot those issues that cause the burners off while the pilot light is lit. Generally, a failed automatic shut-off, defective gas valve, and rusty thermocouple cause the burners won’t ignite when the pilot light is still on.
Below we also include other culprits behind this problem and provide their solutions. So, stick with us till the end.
Table of Contents
Why the Pilot Light Lit But Burners Won’t Ignite?
Multiple reasons are responsible for your furnace burner not igniting when the pilot light is lit. Below we include several reasons behind this issue and offer solutions to them.
01. Defective Gas Control Valve
If the gas control valve is faulty, your burner won’t ignite. Due to the defective gas control valve, the main burner won’t light as the electronics in the valve fails to recognize the pilot is lit.
How to Fix:
Unfortunately, you can get no luck if the problem is within your gas control valve. You can find any serviceable parts in the market. So, you need to replace the whole assembly.
02. Thermopile is Not Sensing the Flame
We bet your pilot is lighting correctly, but the burner won’t light. It happens when the thermopile of your burner is not sensing the flame. Maybe the thermopile gets covered or buried with rust & corrosion.
How to Fix:
First off, take a multimeter and measure the output of your thermopile. The thermopile output should be at least 350mV. If you get less than 350mV, bring the thermopile out from the burner. Then, clean the rust & corrosion build-up from it.
03. Corrored Burner Line & Jet
You don’t need to replace the whole assembly unless you check the main burner, line, and jet. The main burner won’t ignite if its line and jet get corroded with dust, debris, and dirt.
How to Fix:
Remove the burner from your water heater. Then, inspect the burner line and jet. If the burner line & jet get rusty, take an air compressor and blow out the corrosion and rust. We hope it will work and let your burner light up.
04. Maybe the Automatic Vent is Closed
Whether you own a gas boiler or a water burner, most of them have vents. If they remain closed, your water heater won’t ignite. Plus, most gas burners have two switches- one flame roll-out switch and a flue gas spill switch. If they get faulty, the main burner also doesn’t light.
How to Fix:
Make sure the automatic vents of your burner are open. It will be an easy fix if your boiler won’t turn on due to the closed vents. Also, don’t forget to check out the switches of your gas or water heater. If any of them get faulty, replace them with a new one.
05. Rusty Thermocouple
The burner won’t light if the thermocouple gets rusty or buried in corrosion. When the thermocouple gets corroded, it can affect the temperature. Consequently, it doesn’t let your burner work properly.
How to Fix:
The easy fix to remove the rust & corrosion from the thermocouple is to clean them off with a vacuum. You can use a vacuum with a brush attachment to brush away dirt and debris from on and around the thermocouple.
Keep in mind; the burner area will be red hot. Before vacuuming the thermocouple, make sure the unit is completely cool. Otherwise, there is a chance of fire hazards.
After cleaning the thermocouple, replace it. If cleaning doesn’t work, have a new thermocouple and replace it.
And remember, sometimes you may find, after replacing the thermocouple, the pilot still doesn’t ignite. In such a case, you can read our solution guide on pilot light won’t stay lit after replacing the thermocouple. We hope you will get the solution.
06. A Failed Automatic Shut Off
On rare occasions, the pilot will remain on but the burner fails to ignite. However, we figure out another issue besides the other reasons behind it. And the reason is- the pilot shut-off doesn’t shut down when the burner’s safety does. It’s also known to us as a failed automatic shut-off.
How to Fix:
First off, use a screwdriver and hard tap the control valve. It will help to displace the tiny disk and the pilot light will go off. If you fail to pull out the tiny disk, set the control knob to the off position.
Then, turn the dial of your control knob off to shut the pilot light off. Once you remove the pilot, bring the thermocouple out from the unit. And get a new one and install the thermocouple to fix the issue.
Do all gas furnaces use a pilot light to ignite the burner?
No, all gas furnaces don’t use a pilot light to ignite the burner. The newer models use an electric ignition system to turn the burner on.
Will a bad thermocouple keep a pilot light from lighting?
Yes, a defective thermocouple keeps a pilot light from lighting as it turns the gas supply and electric signal off both to the pilot and control valve.
How do you fix a thermocouple?
If a thermocouple gets rusty, you can use a brush attachment to clean it. On the other hand, you should replace it if cleaning the thermocouple will not bring any good to it.
Why is my gas fireplace not coming on?
First off, check the breakers box. If the breakers get tripped, your gas fireplace will not come on. Also, a defective gas valve is responsible for not having your gas fireplace turned on.
What do you do when your gas fireplace won’t light?
First off, troubleshoot the problems that cause your gas fireplace won’t light. A faulty spark ignitor, defective gas valve, and rusty heating element are some issues behind a malfunctioning gas fireplace. So, fix those issues to turn on your gas fireplace.
Your burner or water heater won’t ignite due to the defective thermocouple, faulty gas valve, and closed vent.
Fortunately, we have discussed how to solve those issues. So, follow the guideline we have enlisted above to fix the problems. However, if you fail to ignite your burner following the methods we mentioned, let us know in the comment box. We’ll come back ASAP with a solution.