Why Your Furnace Pilot Light Won’t Stay Lit? Causes And Troubleshooting

A furnace pilot light is what drives the flame of your furnace, especially if you have an older, natural gas-driven furnace. These operate on the basis of a small blue light that appears when the furnace turns on. Its functioning is pretty simple. 

Upon the furnace being turned on, a natural gas is released into the burner through the valve. The natural gas interacts with the blue pilot flame, which leads to the formation of an actual flame.

You’ll find this technology easily observable in appliances like gas stoves. However, the working of a pilot light in a furnace is also similar. A small amount of gas is usually released through a small tube, which, when lit, becomes ignited. 

The pilot light, however, can be dangerous and risky. In case the pilot flame dissipates, the gas coming from the tube (if it’s not switched off) would collect in the air.

And if it was suddenly ignited by any means, all the gas in the air would be lit, and this could cause an explosion. Of course, many devices that use this mechanism have safety nets that will troubleshoot this problem if it was to occur. 

However, if you’re having problems where your furnace pilot light won’t stay lit, the tips below could help you understand why. However, owning a gas driven furnace is a pretty old venture in itself, so the problem might lie in the fact that you’re using a furnace before it’s time.

Yet, if you want to repair your furnace and keep it going for a few more winters, we have some possible causes of furnace pilot lighting problems, and some solutions listed below.

Causes Why Your Furnace Pilot Light Won’t Stay Lit

Some universal causes for which your furnace pilot light might be failing you is as follows:

Bad Or Worn Out Thermocouple

We mentioned before that if your pilot light goes out, it might cause the gas to spread into the air and increase the chances for a burst of explosion.

The thermocouple is one such device which takes the measures to prevent a thing like this from happening. If there’s no flame or a pilot light, the thermocouple will generally signal the gas valve to close. 

However, if your thermocouple is old or worn out or hasn’t been working properly, it might be sending the gas valve incorrect signals when the pilot flame is still on. This leads to the gas being cut off, and the pilot flame disappearing. 


In case of a bad thermocouple, you might have to do some research and digging to pinpoint the root of your troubles. One of the first things you should check is whether your thermocouple is aligned above the spot where your pilot flame lights up. 

Since the thermocouple is a flame sensor, any misalignment would stop it from getting a correct read of the flame, and thus, a wrong signal would be sent to the gas valves.

This might happen because of sudden movements of your furnace that might have displaced the thermocouple. If this applies to you, make sure to fix the positioning, and also that the screw holding the thermocouple is nice and tight. 

If there’s no signs of misalignment, and rather, everything seems to be in order with the placement- it’s possible that your thermocouple is due for a cleaning. A dirty thermocouple messes with the sensory functions and dulls them. And so, the sensor might not be able to detect the pilot light and cause the gas valve to shut off. 

Another aspect to explore with respect to your thermocouple is whether it’s simply- bad at detecting heat. For this, you can use a multimeter to test the number of millivolts identified when you put heat near the flame sensor.

Usually, any heat should make your thermocouple run up to a millivolt range between 18 and 35, but if your thermocouple fails to reach even 18 millivolts, you should consider replacing the part, as it’s simply inefficient. 

Dirty Furnace

Bad Maintenance is the leading factor behind the problems of many household appliances. This is especially true for dirt, which, when gathered at a place, causes considerable trouble in the functioning of any unit. Similarly, if there’s dirt in the orifice of the furnace, this might be weakening the pilot flame. 

A weak pilot flame can easily stop being lit. To detect signs of weak flame, and dirt, take note of the colour of the flame. 

If your pilot flame is blue, but tiny and inconsistent, or if your pilot flame is yellow or yellowish orange, it indicates a weak flame. Ideally, your pilot flame should be a clear, rich blue colour, small, but not small enough to disappear. 


If it is a dirty orifice that’s holding your pilot light flame back, you need to start cleaning. First, follow all safety precautions and turn off the gas valve, etc. You can clean your unit by the gas tube, through which you can blow some air. You can also clean the orifice by using a needle or something just as thin and small that can fit in the hole in the orifice through which the gas travels. 

If you’re reluctant to get handsy with your pilot, it might be better for you to take the unit to a local parts or hardware servicing store that will clean it for you.

You can consider getting your entire furnace serviced by furnace companies, that will clean the entire unit including the pilot. This can get pricey, but it’s worth it for the smooth, as good as new furnace you’ll be able to use after. 


The gas regulator, usually located outside of your house, is what supplies gas to all the gas driven appliances inside. The problem arises if your gas regulator is damaged, or if your gas line is bent, as this messes with the flow of natural gas into your appliances. 

In this case, you’ll usually find that the flame on all your gas appliances like the stove, or the drier or the furnace is weak and inconsistent, because the lines aren’t able to provide the units with sufficient amount of gas. 

So, if you find all the gas powered units in your home equally malfunctioning, take a trip outside to inspect the gas regulator or the gas lines. 


If you are dealing with a problematic gas regulator or a bent gas line, this is a problem you should take to your local gas provider- and fast. If you’ve got no expertise in this area, it’s going to be hard to diagnose whether the issue is serious or not. This is why it’s advisable that you immediately seek out a professional. 

Wind Interfering With Pilot Flame

This is one of the easiest and simplest causes to a pilot flame that won’t stay lit. This probably wouldn’t be the first thought in your mind, because human beings tend to overcomplicate things at the smallest signs. But, we advise you to check your windows and doors and see if you’re allowing any wind or breeze to flow through the gaps into your home. 

A strong inflow of air could simply exhaust the flame, as a pilot is usually small and easy to put out, but they can stay lit for a few hours to days consistently. So, ensure that there’s no draft of wind incoming that’s disrupting the course of your warm afternoons by blowing out the pilot flame.


If a draft of wind from the window is ruining your perfectly good day, all you need to do is find the willpower to shut window and door openings, and make sure there are no gaps allowing wind to enter your home and disturb the working of your furnace.


Before you explore all these options, make sure that you’ve tried to also relight your pilot light by yourself when it goes off. For this, you’d have to push and hold a button that opens the valve. 

Then, light the pilot flame and wait for a few seconds until the thermocouple heats up. Once you release the button now, if the pilot light still doesn’t persist to stay lit- then it’s perhaps time for a general furnace check-up. 

A good furnace pilot light will ensure the safe and comfortable functioning of your furnace. The above causes could go a long way in helping you figure out what is wrong with your furnace, and these solutions could fix that too!

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