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Question DetailsAsked on 11/15/2017

The pilot on my fireplace, when the fireplace is off makes an odd 'poof' sound and jumps a bit.

The pilot on my fireplace, when the fireplace is off makes an odd 'poof' sound and jumps a bit. It looks like it's hitting the grate under the logs. I am leery to leave it connected to the gas. Is this normal?

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Voted Best Answer

No, not at all normal. The poofing sound is a small pocket of natural gas exploding - a bit of gas building up unburned, then igniting and exploding (and if it is the pilot is going out, commonly reigniting it at the same time) as the edge of the gas cloud reaches the pilot flame or a firelog or such which is hot enough to ignite it - definitely not something it should be doing.

Could be caused by any of several things. I am going to assume you have a relatively modern (say 1970's or later) fireplace, so it uses a thermocouple or thermopile to power the gas control valvea and shut it off if the pilot goes out - not just a free-burning pilot light without safety control on it. (Thermocouple/thermopile will be a very thin copper tube leading to the pilot fitting, in addiiton to the pilot gas supply tube (which is usually aluminum or steel) - looks like this - the copper tube with the straight shaft sticking up next to the pilot flare fitting (which would have a pilot gas supply tube screwedinto the bottom of it, at the left):

1) very low pilot gas pressure allowing the pilot flame to be easily blown out by drafts in the firebox,

2) pilot housing where the gas comes out is surrounded by soot, rust, debris or ash or such causing the gas to diffuse at the discharge point and intermittently lose contact with the flame then reignite, or to cool so much as the flame burns through the debris that while burning it intermittently causes the thermocouple to cool off enough it shuts off the gas flow,

3) thermocouple/thermopile failing so is intermittently dropping below the necessary self-generated power which keeps the gas flowing, so pilot gas flow is intermittently cutting off, then back on as the residual pilot gas reignites and reheatds the tip

4) thermocouple/thermopile not fully in the flame - not far enough into it or too far off to the side, or pilot diffuser is turned to the side, so it is cutting the gas flow off intermittently as per 3) above,

5) rarely, gas control valve failure, like internal springs getting weak with age,

6) a gas leak in the tubing leading to the pilot fixture or at the gas shutoff valve next to the fireplace, which creates a pocket of gas which then explodes when it contacts the pilot flame or hot metal or log or such

Regardless, not a good thing and while your thermocouple/thermopile SHOULD in theory shut offr the gas if the pilot went out for more than a second or few, no guarantees - and if caused by a leak the leak could increase. I would shut off the gas shutoff valve next to the fireplace (either turn to OFF if an OFF - PILOT - ON valve, or if the following type turn 1/4 turn so the handle is crosswise to the pipe instead of aligned with it.


Might also have a key-operated valve in the stone/brickwork around the fireplace, like this - which also turns 1/4 turn to turn off (may turn both or only one direction to off).

You could try cleaning around the pilot and lightly bronze wire brushing the end of the pilot gas tube and the tip of the thermocouple to clean them up - if that solve it probably just dirted up.

Otherwise, Heating and A/C would be the normal Search the List category for this - some Plumbing contractors who also do gas heating system install/repair also do this type of work.

I would shut off the gas valve and the power switch (if a power switch) till it is fixed. If you shut it off and then start to smell gas, ventilate the room well and call the gas supply company emergency number to get them to check out where the leak is - generally (though some gas companies also do gas appliance/fireplace repairs) they will not repair it but will get it shut off to be safe till a repair is effected. If a significant leak (not likely since your a poof rather than a big whoosh) then shut off the main gas supply also - sometimes one before the gas control valve if you have one, otherwise the main one just below your outdoor gas meter - though fo course that also takes out all other gas-fired appliances and water heater and furnace and such.

Answered 2 years ago by LCD

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