gas smell - dont understand

[timjimbob]

Confused by this.
Have a attic system. The supply vents register high natural gas levels and it smells like it. Likewise, flue has high levels.
I read zero on the co detector and cannot find NG level anywhere at the burners. I also checked the attic and short return ducting for any gas. None.
I guess I have a bad heat exchanger, but I would expect a high reading on CO, not NG. Flame looks good.

[rundawg]

Confused by this.
Have a attic system. The supply vents register high natural gas levels and it smells like it. Likewise, flue has high levels.
I read zero on the co detector and cannot find NG level anywhere at the burners. I also checked the attic and short return ducting for any gas. None.
I guess I have a bad heat exchanger, but I would expect a high reading on CO, not NG. Flame looks good.

What is the CO level in the flue?

Is the CO reading Stable?

Does the CO continue to rise on Shutdown or decrease to zero?

Do the O2 levels change when the blower comes on?

Model Number of this unit please.

[timjimbob]

O2 Oxogen??.

[rundawg]

O2 Oxogen??.

Yes. O2 percentage from a combustion test.

[timjimbob]

"Does the CO continue to rise on Shutdown or decrease to zero?" What is the significance of this question?

[rundawg]

"Does the CO continue to rise on Shutdown or decrease to zero?" What is the significance of this question?

Tells you if the gas valve is leaking after shutdown.

[timjimbob]

Wouldn't I want to check combustion gas level, not CO?

[rundawg]

Wouldn't I want to check combustion gas level, not CO?

Doing both would be prudent.

[Jim Davis]

How did you measure gas in the flue? What testers are you using?

[timjimbob]

used fieldpeice combustion gas meter a foot from the termination. Real high.

[Jim Davis]

Fieldpiece does not make a natural gas leak detector. What is the model #?

[timjimbob]

Infocon Gas-mate and fieldpiece scm4

[Jim Davis]

Is the furnace running when you detect gas in the flue? Any chance there is some type of battery charger in the house?

[timjimbob]

Only detects gas when unit if firing. Nothing on "fan only" Vacant house. No painters, or chargers.

[timjimbob]

REplaced system.. had a chance to tear into the furnace and heat exchanger. No rust and all gromets seem tight. I guess I will never know what happened now.

[kjbhvacr]

Mustg be a link Dangerous!

[Jim Davis]

Most gas leak detectors are temperature sensitive. They will react to changes in temperature alone.

[lzenglish]

Never discount the possibility of a dry "P" trap emitting sewer gas. Remember that natural gas is odorless, except for the odorizer that is added to it, and some sewer gas methane can get real close that smell. I have been fooled before....just sayin.

[timjimbob]

Never discount the possibility of a dry "P" trap emitting sewer gas. Remember that natural gas is odorless, except for the odorizer that is added to it, and some sewer gas methane can get real close that smell. I have been fooled before....just sayin.

I always check this out, but I didn't consider on a positive pressure system. It had no trap. Too late know I should have checked.

[lzenglish]

I always check this out, but I didn't consider on a positive pressure system. It had no trap. Too late know I should have checked.

An Attic Air handler with "NO "P" TRAP"? Gee, that's "ODD".....!!!!And just what is a Residential "Positive Pressure System", as opposed to a "Standard Residential System"? Not trying to throw rocks, just offering up more food for thought. Take Care..