Author Topic: Periodic Gas Smell  (Read 8081 times)

inNeedOfHelp

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Periodic Gas Smell
« on: January 19, 2009, 09:16:29 AM »
I have a problem that 2 HVAC techs have not been able to help me with.  My furnace seems to leak a small amount of gas after the end of the burn cycle. I had an emergency tech from the gas company come over and he could not detect any gas on his meter until he placed the sensors probe near the manifold outlets. It seems that there is a small amount of residue gas that is left over after the gas valve shuts. At first the guy from the gas company wanted to tag the furnace but we noticed that the meter ran high for only a few seconds (enough for you to smell the gas if you were close enough) and then it went to zero.  He suggested that maybe we get a new valve, which we did (we got someone else to do this). The problem was still there, so we called the gas company again. Again the tech said it had to be the valve. I said that probably doesn't make sense as we just replaced it. Does anyone know if its normal for some furnaces to emit a small amount of gas at the end of its burn cycle? Is it possible that there is enough of it left over in the manifold that we could smell it or should we never be able to smell any gas and that this is a sign of other problems?

Offline Admin

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Re: Periodic Gas Smell
« Reply #1 on: January 19, 2009, 02:42:55 PM »
There should never be left over gas, or a smell of gas period.

Keep calling back the company that replaced the gas valve until they figure it out.  It seems like the problem was mis-diagnosed and the gas valve was replaced for no reason.






Offline Zzz

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Re: Periodic Gas Smell
« Reply #2 on: January 19, 2009, 08:40:06 PM »
I read an article from Honeywell that said the small residue of gas smelt from furnaces was the time it took the induced draft fan to shut off was to short and you were smelling the exhaust dwafting back out the heat exchanger, I thought B"S your just covering your leaky valves but, maybe it was your brand of furnace they used to check. Give me some details on your furnace and I'll help if I can. Are your fresh air intakes clean outside were the hood is? Could this smell be coming out your draft hood on the water heater?
NO YOU SHOULD NEVER SMELL GAS !!! If you do there is something wrong.

Offline PeterT

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Re: Periodic Gas Smell
« Reply #3 on: January 19, 2009, 08:49:25 PM »
I had a High efficient Ruud and everytime it shut down my TPI721 would go off at the side of the fresh air intake. And then read 0 right away. I told the home owner we could pipe it outside so that the fresh air was brought in from outside. I did this over and over everytime the call for heat was met the flames would go out and the meter goose next in the freshair intake would go off and stop right away. There was no leakage after that the meter running in side the furnace would not pick up anything.

Offline Zzz

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Re: Periodic Gas Smell
« Reply #4 on: January 19, 2009, 09:13:00 PM »
Thanx Pete these kind of things make us all better at what we do.
They might seem goofy but you spent the time and now I don't have to.

inNeedOfHelp

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Re: Periodic Gas Smell
« Reply #5 on: January 20, 2009, 09:26:38 AM »
The exhaust pipes to the outside look clean. I would like to add that the smell comes directly from the area just behind the manifold pipe whose outlets blow gas towards what I believe is the heat exchanger ( I apologize if I get the terms incorrect as I'm not well versed in the technical workings of a furnace). If I get close enough to this manifold, I notice a slight backdraft of air towards my face at the end of the burn cycle. This is when I smell the gas. It's as if there some gas left in the heat exchanger or manifold or the area in between that gets blown back. Does this make sense? What should I do next to resolve this problem. I really appreciate the responses this post has already received.

Offline Admin

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Re: Periodic Gas Smell
« Reply #6 on: January 20, 2009, 05:20:01 PM »
The ventor motor should continue to run after the burners have gone off, and that motor should exhaust all the products of combustion.

What is the make and model of your furnace?