Why the Fire in a Gas Boiler Extinguished By Itself?

I would like to know what was the reason why the fire in a gas boiler can be extinguished by itself. I have a relatively old boiler that runs by natural gas to heat water for my baseboard heating units. A couple days ago, somehow the fire in the boiler extinguished by itself -- no fire, not even the pilot. The control switch was at the "ON" position. But I didn't smell any gas. I can re-ignite the boiler without any problem, and the problem has not returned; this is good. But I would like to know why the fire in the boiler would be extinguished in the first place.
I have the following specific questions:
- Would this happen when the natural gas supply was momentarily running out of gas? But the fire in my relatively new water heater was still burning while the fire in the boiler was extinguished. If the natural gas supply was momentarily stopped, I would assume that the fire in both the boiler and the water heater would be extinguished, right?
- Is the boiler smart enough to automatically switch off the gas supply when it senses that the fire is extinguished? I am asking this because the control switch was at the "ON" position but I didn't smell any gas.
- Will this happen when someone (like my 2-year-old child) toggles the power switch of the boiler Off and On?
Thanks in advance for any info.
Jay Chan
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snipped-for-privacy@hotmail.com wrote:

You bet! There should be a thermocouple (it looks like a closed metal tube) sticking in the pilot flame. It senses the pilot and if it does not sense a pilot flame or if the thermocouple fails it turns the gas off to both the main burner and the pilot. They are cheap and easy to replace. What you are observing is common when one is getting old. You can also try cleaning it and or adjusting it to make sure it is in the hot part of the flame. However they are cheap enough, most people just replace them.

It could under some circumstances, but don't blame the little guy yet.

--
Joseph Meehan

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Joseph Meehan wrote:

Now, I understand what the "thermocouple" is for. I only knew that the thermocouple is quite troublesome that I need to replace it almost every year. I didn't really know what it is for. Now, I understand what it is for and the reason why I didn't smell gas even when the switch was at the "ON" position.
My little kid is still not off the hook yet. He is the kind of kid who likes to toggle on/off any switch that he can have access, open all the drawers in the kitchen, ...etc.
Jay Chan
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Yes, if your gas supply was interrupted, the boiler would shut off. This is VERY unlikely and probably isn't your problem.

Yes, there is usually a thermocouple or sensor above the pilot flame (in pilot ignited appliances like most older boilers and water heaters). When that cools off, the gas supply is shut off. This is why you need to hold the pilot button on many newer gas burners for a few seconds after lighting to make sure the gas stays on while the thermocouple heats up.

It's possible, does your 2yo spend much time near the boiler? Having a 2yo myself, it's something I would strongly discourage, with locked doors if necessary.
If I had to guess, I'd guess you experienced some unusually high winds recently, as did a large portion of the USA. Occasionally, a wind that is unusually high or from a different direction than you are used to will cause a backdraft down the chimney that can actually blow out a pilot flame just like blowing out a birthday candle. When the pilot goes out, the thermocouple cools down, and shuts off the gas supply until someone comes along and relights it.
You may want to have your chimney and boiler inspected. In addition to occasionally blowing out the pilot flame, this can also force combustion gases (like carbon monoxide) into the house instead of going up the chimney like they're supposed to. An infrequent occurance may be just due to unusually windy conditions, but having your system checked out by a professional would be the smart thing to do.
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I'd have it looked at by some local boiler or hvac slack jaw. There are plenty of reasons the boiler could have shut down....dont know exactly how your boiler is set up but most gas equipment is equipped with several "safeties" which will shut the thing completely down in the event things are not running right.
Could be a thermocouple gone bad but it could also be other things....we just dont have enough info on your particular piece of equipment to know.
~:>
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oh yes.... your 2 yr old should be able to get around a piece of equipment like a boiler....almost makes me now wonder if this is a troll post.
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snipped-for-privacy@hotmail.com wrote:

There are two power switches to the boiler. One of them is inside the entrance of the side door. I don't know why the boiler needs a second power switch near the side door. I have a feeling that it is an emergency shutoff or something like that.
Jay Chan
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snipped-for-privacy@hotmail.com wrote:

Yes, the boiler has a thermocouple, and it goes bad every year for some unknown reason. I am trying to extend its life by shutting off the pilot light when we are not in heating season; but I don't usually remember doing this.
Seem like the thermocouple is what shut off the gas supply when the flame is out. This explains the reason why I didn't smell any gas even when I saw that the control switch was at the "ON" position.
Jay Chan
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louie wrote:

OK, you are probably right. If that was the case, I would assume that the fire in both the boiler and the water heater should have been extinguished.

Thanks for the explanation of the role of thermocouple in keeping the gas supply shut off when the flame was extinguished.

There are two power switches for the boiler. One is in the basement right next to the boiler, another one is right inside the entrance of the side door that is the primary thruway in and out of my house. Therefore, this is quite easy for the kid to toggling Off and On the power switch without being detected when I am bending down putting on the shoes for the kids. I don't know why we have a second power switch near the side door. May be it is an emergency shutoff or something.

Yes, you are right. The temperature in our area dropped significantly in the evening when the flame of the boiler was extinguished; I am sure there were high wind when there was cold front going through. And you probably are on to something. But because we are in the heating season, the boiler is on all the time (just a matter of high or low flame). Even if the pilot light was blown off, the main flame should not be blown off that easy right? And if the main flame was there, the main flame should be able to re-ignite the pilot light (afterall, they are right next to each other), right?
Anyway, I will go back home after work at around 5:00pm and check the flame in the boiler to see if the main flame is ON or not. Normally, the house should be quite warm at that time after a whole day sun shine and a whole day of human activities inside the house. If the house is warm enough for the main flame to go off, I should be able to observe this at that time.

Yes, you are right. I believe we should have the boiler inspected and cleaned every year. Thanks for reminding me about this.
Jay Chan
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you can buy cheap switch cover at electrical supply house so no one can move a regular wall switch without a screwdriver. that might help with your child.
a good friend has a 2 year old he is into everything
they say smart kids are worse perhaps that info helps a bit
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snipped-for-privacy@aol.com wrote:

I am hoping that he will out grow his bad habit. But a cover on the switch that requires some force to open the cover is a good idea -- not only good for preventing the little kid from fooling around the switch, but also preventing the adults from mistaking it as the light switch.

Thanks for the encouragement.
Jay Chan
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