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My Pilot Light Will Not Stay Lit

This section is a tutorial on how to keep your pilot light to stay lit once you initially light it.  If you cannot get your pilot to light, please refer to the How to Light Your Pilot Light Tutorial.

 

 

There are a few reasons why a pilot light will not stay lit. But before we explore them, we should first learn how a pilot light works.  For a more detailed description of how gas fireplaces work please visit our Fireplaces 101 page.  But before continuing with this tutorial, I highly recommend checking out the how a pilot light works link.

 

If your pilot light will not stay lit, it can only be 3 problems.

  1. Your pilot flame is bad
  2. Your thermocouple sensor is bad
  3. Your main control valve is bad

Just from experience, 99% of the time, the first two are the case.  It is very rare for a main control valve to go bad (although occasionally it does happen).  The good news is that each of these parts can be tested!

Personal Note: The fact that we can test components is very important.  Many times I would find that many “professional” fireplace service or heating and cooling companies would not know how to test these components.  I would often be the second or third company called to try to fix somebody’s gas fireplace after other companies were unsuccessful.  In fact, my training when I started servicing fireplaces consisted of a “replace parts until it works” strategy which some companies often employ.  This is part of the reason why I created the Find Certified Technicians page; so that if you choose to hire a professional you are more likely to get someone who knows what they are doing.

  1.  How to test of your pilot flame is bad

This is probably the easiest of the tests, and it doesn’t require any equipment.  You just need to visually inspect your pilot light.  It should be blue, without much yellow in it at all.


Time to Complete:  >5 minutes

Recommended Tools

  • Your Eyes

 

A healthy pilot flame should look like this:

It should be blue, and the flame should engulf the sensors and almost wrap around them.  This is important because those sensors need to be a certain temperature.  If the flame is yellow:

this is not a good thing.  Yellow flames seem to pull away from the sensors as the flame shoots straight up in the air.

The easiest way to describe it:

A healthy pilot flame will be much like a blue  “blow torch” flame. It will shoot sideways and be directly on your thermocouple and thermopile sensors. An unhealthy yellow flame is more like a “candle”. It will shoot straight up in the air and may not engulf your sensors.

If the flame is not healthy, it will not engulf the thermocouple or thermopile and the result: a pilot that wont stay lit once you stop pressing in the pilot knob.

If you determine that you have a bad pilot flame, you can either clean out your current one with a wire brush (cheap but not long term) or replace the pilot assembly (orifice and hood).  This takes a little more time but will last much longer.  Find out your Make/Brand and model of your fireplace.  You can visit the What Kind of Fireplace do I Have page if you are having trouble.  Most fireplace brands will a website where you can locate a local dealer to order a new pilot assembly.

 

2.) How to Test Your Thermocouple Sensor

If your pilot flame looks good, chances are you have a bad thermocouple sensor.

This sensor controls the pilot flame.  Again, please refer to the how a pilot light works section if you do not know which one is the case.

For this test we will need a device to test voltage.  As we learned in the how a pilot light works section, these sensors create a small amount of voltage.  By testing the voltage on your thermocouple, you can determine if it is malfunctioning.

 

Time to Complete:  15 minutes

Recommended Tools

Here are a few tools that I recommend.

 

For this tutorial, I am using the Gardner Bender Digital Multimeter .  You can purchase this through my affiliate link above for about $18.00,  otherwise I have used this one before which runs about $2.00.  The $2 one should do the trick but I have had it give me false readings before, so just keep that in mind.

Also, you basically just need a 7/16” wrench.  The jumper wires just make it easier for testing.

First, you want to locate your main control valve.  This is the same control valve that you use to light your pilot.

Gas fireplace main control valve

Next, you’ll want to locate the thermocouple sensor.  Thermocouples are almost always made out of copper.  Most of the time it is located in the front of the valve, but sometimes it can be in the rear.  The easiest way to find it is to take a flashlight and look for a tube that looks copper.  It will always connect back to the valve somewhere with a brass fitting.

 

 

Gas fireplaces do not have any power connected to the valve so there should be no worry about shocking yourself.  The only component that is plugged into power would be a the fan system which should not be in the way for testing the thermocouple.  Most of the time, you can always unplug the fan if you are worried about this.

Once you’ve located where the thermocouple connects to the main control valve, you need to disconnect it.

This is where you want to use your 7/16″ wrench (this is also where a short one comes in handy).  Simply loosen the fitting at the control valve and disconnect it from the valve.   You may have to gently bend it to get at the fitting.

 

 

Once you have it disconnected you will want to take your jumper wires and hook them onto the thermocouple.  You want to clip one onto the very tip and one somewhere on the copper tube like this:

 

 

Then we want to connect the other ends of the jumper wires on to the test leads of your meter like this:

 

Multimeter testing thermocouple

 

It does not matter which jumper wire goes on which testing lead.  If you have them backwards, when we get to testing,  it will just show a negative symbol before the voltage reading but the reading will be the same.

Next, we want to turn our meter on and turn it to the 2000m (millivolt) DC setting.  If you are using the Gardner Bender Digital Multimeter, it should look like this:

 

digital multimeter gas fireplace repair

 

If you are using another device, instead of the “V” symbol, it may say DC or have the same “solid line with dashed lines underneath” symbol.  Now that the meter is on and everything is connected we must now light the pilot.  Refer to the How to Light Your Pilot Light tutorial if you are unfamiliar with this.

Now we just light the pilot like normal only this time when the pilot ignites (because the thermocouple is disconnected) it will not stay lit on its own.  You must light it and continue to hold in the pilot knob while you read the voltage.

The voltage on the thermocouple should keep climbing until it reaches somewhere around 25 millivolts as shown above.

I’ve seen fireplaces closer to 30 mv and also closer to 20 mv still function correctly.  If you have a reading around 20 or below, you should change the thermocouple.

 

I will post a tutorial on how to fix these problems shortly.  Thank you for visiting and please return!

22 Comments
  1. Thanks

  2. I have a Kingsman ZVFB3633MVP fireplace, and I can’t get the pilot lite to stay lit. It lights when I have the pilot button pushed in, but it goes out as soon as I release it. The flame is blue. I have replaced my theropile, and it is producing about 550mv. When I turn on the switch, it cuts the voltage in half like it’s supposed to. I do not seem to have a thermocouple on this system. What is the next troubleshooting step? Thanks in advance.

    • This is a vent-free fireplace which has a ODS (oxygen depletion sensor). It is most likely the ODS that is malfunctioning.

    • Clean the ODS pilot air inlet hole as per the installation manual. 9 times out of 10 this is the problem. Should be done yearly.

  3. My pilot light will not stay lit when I release the pilot button. I have replaced the thermopile, and the new one is producing 550 millivolts. The pilot flame is blue (with a little yellow at the tip), and the switch is working (voltage cuts in half when flipped). I do not have a thermocouple on this Kingsman fireplace. What is the next troubleshooting step? Thank you in advance.

    • It sounds like your pilot flame is good and the thermopile is operating correctly. Is the thermopile hooked up directly to the gas valve? Is it on the correct ports? How are you getting a voltage drop with the switch if the pilot wont stay lit? Or you may have a spill sensor (a little heat sensor disc usually located near the top of the fireplace). If this is tripped the pilot will not stay lit. What is the make and model of the fireplace?

  4. Hello-

    Great tutorial, thanks –

    Two (2) questions:
    1) how do I replace the thermocouple?
    2) where can I get one?

    Thank you.

    • I will be posting a tutorial on this later. But basically it unscrews from the bottom of the pilot assembly bracket, and unscrews from the main control valve. You can buy one online (check for your fireplace brand and model number) or at your local fireplace store. I think even the big box stores might have them.

  5. Is it possible for the thermocouple to be welded onto the stem from which the pilot comes out? There is a wire (insulated, copper color) going from here to the back of the control and attached with a brass fitting. It just doesn’t seem like the correct placement for the thermocouple because there is no way the flame would reach that part. There is a separate thermopile, which I replaced but the pilot still won’t stay lit. Pilot is nice and blue. Please help! I can send you pics of what I am talking about if you have an email address that I can send them to. Appreciate your help!

    -Dinesh
    PS-Are thermopiles all the same? I bought a Honeywell powerpile 750 millivolt that connects via spade terminals, looks like my old one.

  6. There is a fourth thing that could go wrong as I found out today. It is the limit switch. These are found on older units. I had replaced my thermocoupler and still the pilot light would not stay on. So I thought that it was the main valve and decided that I would have a professional work on it. When the HVAC guy tested it out, he said that the thermocoupler was fine; the valve was fine, the culprit was the limit switch. He will have to order the part because they don’t carry those anymore. My unit was built in 1991. So my advice is to check the limit switch. It costs a lot less than a valve.

    • I have an older system with the same problem. Where do I find and test the limit switch?

      • The limit switch will be in line with your thermopile. Start at the valve where the thermopile connections are and follow them back to the pilot assembly inside the fireplace. The limit switch acts as an interrupter, breaking the connection of the thermopile back to the valve.

  7. I cleaned the pilot housing and now have a blue flame. The pilot stays on. But, when I turn the gas valve to full flame the flame jumps to the brass gas nozzle and creates a flame in the long supply line to the flame plate. What is wrong?

    • It sounds like your burners may be plugged. Prolonged firing of your gas log can cause the sand in your burner pan to melt and plug up the holes in your burner. This forces the flame back out the side of the pan and it flares up through the air shutter. Try vacuuming out your burner pan and replace the sand and embers with new sand and embers.

  8. I have a gas fireplace, not sure of the exact model at the moment and my issue is that I have a strong blue pilot flame, the pilot stays burning continuously as it should. When I turn on the fireplace the flames ignite as they should, but the entire system shuts down after about 2-3 minutes. The flames, pilot, everything goes out. Any ideas? Thank you for your help!

    • If it is a sealed (direct Vent) fireplace, this sounds like a venting issue.

      Does the flame get really blue and lift off the burner (as if its burning in the air)? This would indicate blockage or leakage in your vent so the fireplace is starving for air. Try opening up the glass slightly on the bottom to allow the fireplace to draw room air. If it runs okay with the glass cracked open, you can assume its a venting issue.

  9. Excellent, outstanding web site, I have already fixed my 10 year old Napoleon venting issue and a friends intermittent 3 year old fire place on/off switch. Your 101 training is wonderful. I have shared your site with 5 other individuals and will keep on sharing. Job well done! Thank you!

  10. I have a montigo 36dv rv fireplace the pilot will start and stay running but once I turn my remote electrical switch on I loose my flame. What can I do to fix this??

    • How does your pilot flame look? What kind of voltage are you getting on your thermopile sensor?

  11. My pilot light won’t stay lit
    I’ve changed the thermo couple-the pilot light still won’t stay lit
    I double checked the output of the Thermocouple – I get 21.9 so while it is on the low side of the necessary millivolts, most everything I read requires a minimum of 20 (I didn’t have alligator clips so just held the lead on the thermocouple pinned with my thumbs)
    I checked the output of my thermopile – 550 and climbing
    I removed all the wires and checked the valve function by placing the leads of the ohm meter on the TP and TH terminals – I get 2.0 Ohms (stuff online I’ve seen indicates that for an SIT 820 valve 1.7-2.5 is normal).
    I’ve concluded that it has to be the valve for the pilot side but how can I be sure its the valve before I get a new one? the ohm test would seem to indicate proper valve function on the main gas flow part of the valve along with proper thermopile output would indicate that part of the system is good.

    Is there a test for the valve on the pilot side of things? can the valve be disassembled and the electromagnetic valve fixed? thoughts?

    • On the SIT valve, the thermocouple threads into the valve and will touch a white clip (connected to a blue wire). This clip can be mounted in several places on the valve, so make sure the thermocouple is hitting this clip and you are not screwing it into a different port.

      If this checks out, you will need a new valve as the valve is not a field serviceable part.

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