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Navien Tankless water heater inside gas smell on start up

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Paul_W
Paul_W Member Posts: 2
in Domestic Hot Water
Hello all,
I have a new Navien Tankless water heater installed in the walk in closet las year on 1st floor. The unit works well has no alarms or error codes but we noticed a light gas smell when we use the unit i think its on start up. If we dont use the unit it doesn't smell at all. The vent from the unit is going up 1ft than 90deg than 2ft thru the wall outside. I checked the manual because I thought that maybe the intake is too close to the exhaust and might be sucking air back inside but I don't think that's the case because its is more than 17" apart (per manual) and also i have dropped the exhaust even lower to 3ft and I still can smell gas in the closet.
What could be the cause of it, might be that the unit is just bad?

Comments

  • STEAM DOCTOR
    STEAM DOCTOR Member Posts: 2,557
    If I'm not mistaken, this is a well-known and documented problem with the navians. You probably need a certified tech to call tech support. I don't think they talk to homeowners.
    SuperTechEBEBRATT-Ed
  • dko
    dko Member Posts: 669
    You can smell it with the navien's cover closed?
  • Paul_W
    Paul_W Member Posts: 2
    dko said:

    You can smell it with the navien's cover closed?

    Hello Guys, thank you for replays. Dko actually yes I can smell it with the cover closed.
  • plumbbob333
    plumbbob333 Member Posts: 2
    naviens are known for having leaking heat exchangers
  • CFH
    CFH Member Posts: 93

    CFH Member Posts: 91 January 17

    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.

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