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Navien Boiler natural gas odor when running/ carbon monoxide detected

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CFH
CFH Member Posts: 93
in Gas Heating

1/17/26

Has anyone recently (2026) contacted Navien support about a natural gas odor (mercaptan) when the boiler is running with the cover off? I just spoke to them regarding a NCB 240. I used an Inficon Gas Mate 5ppm gas detector inside the boiler jacket with the cover off and boiler off and did not detect any natural gas. With the boiler running I detected natural gas inside the jacket and then in the room after a few minutes of running. I then checked the exhaust and I had to insert the sensor directly into the exhaust to detect natural gas. The intake and exhaust were approximately 5' apart and separated by a fence. I do not think unburned gas recirculated into the boiler. Navien technical support had some questions about the boiler set up, magnetic separators and other questions that had nothing to do with a natural gas odor but are required to continue technical support. My problem is they required a carbon dioxide detector to check for check for combustion gases around the heat exchanger. I do not believe I was told to check for carbon monoxide instead of carbon dioxide. I understand carbon dioxide is only .4% of the atmosphere and any presence above that would indicate a combustion gas with the boiler running. My combustion analyzer only senses carbon monoxide and oxygen. It calculates carbon dioxide in the combustion gases using the Carbon monoxide and oxygen values. It cannot be used for this test. Does anyone know of a probe type carbon dioxide detector that can be used for this test or is Navien just wasting the plumbers time with these test and forcing the customers to buy a new boiler because the need their heat and hot water working again. I know of 5 boilers in the last year having the same problem. The models varied some were CH models others were NCB. The technician explained the gaskets between the heat exchanger could be leaking between the heats exchangers because it was a negative pressure gas valve.

Mad Dog_2bjohnhy

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 19,881

    Navien is/was having a lot of issues. One issue was the exhaust flue gasket leaking and degrading. There are many U tube videos about this.

    I wouldn't be a bit surprised from what I have heard if they are dancing you around.

    How old is the boiler? Is it under warranty?

    bjohnhy
  • SuperTech
    SuperTech Member Posts: 2,646

    Everything you described is unfortunately normal for Navien boilers. They are notorious for leaking flue gas. With the cover on the boiler it will recirculate the leaking exhaust back through the combustion supply air intake. It's also very common for Navien owners (or their neighbors) to notice a smell of unburned gas from the exhaust. Navien tech support will blame this on a few different things, my opinion is that their boilers are just a poorly made product.

    bjohnhy
  • CFH
    CFH Member Posts: 93

    The boiler has 8 years on the 10 year heat exchanger warranty. I was wondering if the tech misspoke when he asked to check for carbon dioxide and not carbon monoxide. I do not know of any combustion analyzers that have a dedicated carbon dioxide sensor. The come with oxygen and carbon monoxide sensors but not carbon dioxide. They calculate the carbon dioxide based on the other 2 sensors. I did research carbon dioxide detectors but I do not think they will work in this application. I do believe they are giving me the run around. It reminds me when they asked if there was a full port gas valve on the CH 240 boilers when the did not work properly even though the static and running gas pressure were in specifications. Has anyone replaced the leaking gaskets and is it worth the time. Are the other problems found when the gaskets are replaced and how much down time of the boiler is usually involved when gathering all the correct parts to do the job. I have stop taking service calls for Navien because of this.Many plumbers in the supply house have also stopped servicing these boilers because of this. They change a igniter and get a call back on a gas leak. That happened to me three times in the last year. If you do not get support from Navien you cannot run a business installing their boilers. I will put a cast iron boiler and a indirect water heater when possible.

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