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CO mystery


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I belong to ASHI-GLC. Yesterday an email went out to the membership about a problem one of the inspectors was having on one of his jobs. It seems like a real head scratcher. I thought I would post the email her to see if anyone could offer any suggestions.

Just off the phone with an inspector, he is in a house now doing the inspection. Getting very high CO rating (55) whenever he turns on the water?????

Home is on a slab

Electric Water Heater

Furnace is on

Getting this reading throughout the house, but ONLY when he turns on any source of water (ie; washer, kitchen sink, bath sink, etc.)

HELP, have you experienced this? Do you know what is going on?

FYI, levels return to normal when he shuts off the water source.

PS you can respond to this email or text me on the GLC line 734-284-4501

ASHI Great Lakes Chapter

734-284-4501 or carol@greatinspectors.org


Any thoughts on this?


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Is the house on a well? Are the drains properly trapped? Hi levels of hydrogen sulfide gas coming in with the water maybe?

The fact that he'd using a C.O. detector during a routine inspection says that he's got some learning to do. Tell him to learn to inspect without the meter. The meter should only be pulled out when his training gives him cause to suspect there could be something pumping C.O. into the house. If he uses it for every job he's going to find himself constantly chasing false alarms.

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I don't know anything about this place. Here is a follow up email that I got that may help a little:

I have to say, we have the GREATEST group of inspectors around. After putting out the word, my email was flooded with help. Thank you for your assistance.

Here is a recap:

*CO reading of 55, only when water was turned on

*Home was vacant

*Electric Water Heater, Whirlpool

*No known recalls, I checked

*City Water

*CO Meter: Fieldpiece SCM3

Here were some of the suggestions:

-Check the water heater

-Problem seen before, with water in copper pipes that sat for a long time developing CO in line. Ran water thru lines for an hour or so and problem disappeared.

-May be a faulty meter, better equipment. . . .more accurate results

-55 not that high, although should be at 0 (zero). 55 is too high for indoors

-Humidity could be setting off detector, depending on the equipment

-Gas heater could cause back drafting when running water.

-Could be fluoride in the water

-Inspector carries a 2nd detector to verify numbers if they are way off

-Reading of 55 can be achieved when cooking in kitchen

-Is the plumbing stack sharing space with furnace flue? Water turned on can create negative airflow/back draft of running furnace.

-When was the last time the detector was calibrated?

-What are the sources of combustion in the house?

-Is there a wood-burner attached to water system for home heating?

-Possibly the vent fro the water heater, if there is a hole in the vent in pipe or in the chimney

-Call city (water dept) maybe they are working on line and CO is being sucked into the water source.

-Could be coming from water vapor, meter can be sensitive to that

-CO detectors are cross sensitive to other gasses, so it actually may be reading another gas

If conditions had included a Well Water Source:

-Water may have methane from fracking in earth for natural gas drilling

-Could there be natural gas in the well? (this was a common suggestion)

-Could be aerating hydrogen sulfide gas, fooling the meter

-Possibly byproducts of combustion are being sucked into water supply

The city has been called to the inspection site. Our inspector will follow up with his findings in the field. All of theses suggestions were forwarded to him as well.

Thanks again for all of your help!

PS If you need anything you can now text me, on the GLC line. 734-284-4501

Carol Batko, Executive Director

ASHI Great Lakes Chapter

734-284-4501 or carol@greatinspectors.org


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This CO meter has an electrochemical sensor with a filter for SO2 and NO2 so false positives are markedly reduced. Still, it could be H2 causing a false positive.

Is there a funny odor with the water? Could have anaerobic bacteria problem with WH causing SO2 and H2 production. Your symptoms align with this. Consider changing the anode rod then sterilizing the tank with hydrogen peroxide.

Have you held an open flame next to a faucet with the tap opened? CO does not 'develop' in water lines.

I'd try with a full combustion analyzer that has been recently calibrated

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