Natural Gas furnace... whoomp when igniting...

I have a natural gas furnace and most times, when it lights, it lets off an increasingly loud 'whoomp'...
I checked the pilot light and it is up pretty high...
Knowing some basic physics, it is obvious that the gas is filling the chamber and then when the fuel-air mixture hits the right spot, it lights...
I wouldn't really care, but it didn't used to do this...
Jenns
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Jennyfer wrote:

How old is this furnace. No matter. My guess is that the burners are dirty. Call a repairman to diagnose the problem and probably remove and clean or replace the burners. If you leave it like this you could crack the heat exchanger, or worse.
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wrote:

Good thing you know physics. Do you know the one where you hear a loud noise and look down finding yourself 20 ft in the air? Have you thought of having a "tune-em-up, clean-em-up" done to your furnace? Bubba
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The industry term for this is "delayed ignition".
It's a euphemism for a fucking EXPLOSION.
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As some of guys told you, you need proper cleaning in and around the furnace but also check that your location of furnace is not on vacuum in other words if you have clothes dryer in same are make sure your dryer is not creating vacuum in the area or you are having some type of blockage in smoke stack, the items above can spell disaster. Tony

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Wow, that really sounds like a problem. You have my compassion and understanding.
--

Christopher A. Young;
.
.

"Jennyfer" < snipped-for-privacy@hotmail.com> wrote in message
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Jennyfer wrote:

If you have a typical 4-burner furnace, the pilot light will be located between the middle 2 burners. The pilot should have 2 jets pointed in opposite directions directly towards the adjacent burners (burner #2 and #3).
When the main gas valve is turned on, gas flows into all burners, but ignition starts from the pilot and ignites burners 2 and 3, then 1 and 4. What could be happening is that one side (the left or right) is not being ignited by the pilot, or the ignition is not jumping from 3 to 4 or from 2 to 1 until enough gas has filled the burner area to ignite from an un-intended place - and by then there is enough of a gas buildup to create a small explosion.
You'd have to watch the entire ignition sequence (from a safe distance) in order to see what's going on. As has been mentioned, the burners may need to be cleaned (usually - of rust that has fallen from the walls of the heat exchanger onto the burners). The burners should just lift out. Don't do that until you turn off the gas supply to the furnace first.
Another explanation is that there is a hole in one of the chambers and the return air is flooding through the hole into that chamber and disrupting the proper distribution of gas or leaning it out. This would only happen if the fan is already running when the thermostat calls for heat.
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