Wednesday, January 2, 2013

Navien Water Heater Problems

We are having intermittent problems with our tankless water heater. The system is a Navien NR-180A-NG (operates on natural gas). It was installed in December 2010. The system sometimes fails to deliver hot water. Water will flow, but it's cold. This problem only occurs in the winter.

Examination of the control panel indicates the system is in error mode (red light flashing). I didn't note the error code (will do that next time). The system can be restarted by unplugging it and plugging it back in. This morning it took several tries and about 15 minutes to get the system working.

The service tech examined the system and ran some tests, but when he arrived the system was working and he couldn't duplicate the malfunction. He did set an internal recirculation system (we did not get the external recirculation) so the system is supposed to circulate hot water internally from 0600 to 0900 and from 1800 to 2100. This might improve the time it takes to get hot water to various locations in the house, but it's hard to see how it will help the intermittent problem.

One of the theories for why we're having a problem is buildup of condensate in the flue that exhausts hot air from the Navien. The flue piping has a level section that elbows up (see photo) and water could collect here in the winter, since outside air will be cold and make the pipe cold. If enough water is collecting there, it may be blocking exhaust enough so that the system overheats. We'll have to see what the error code tells us next time the system fails.

Vent flue (horizontal) and air intake for tankless water heater.
Flue enters inside wall of garage and goes straight up to roof.
This piping is now contained in a chase.


  1. It’s very frustrating when you can’t detect the problem of your heater. If the problem occurs again, you may need to consider these options: Since you installed it in 2010, maybe it’s about time to replace it with a new one. I know it’s not practical because it may cost a lot. Another option is to seek other professional technicians for a second opinion. Anyway, I just hope your heater is in good condition. But if you’re interested for a second opinion, you can visit this site:

  2. Thank you for sharing this info about Navien Tankless water heaters. Appreciate this share.

  3. Typical reasons for this are.

    Navien Error 10 codes:
    1. Improper venting or a restriction in the vent pipe.

    The entire length of the exhaust pipe must be sloped toward the heater. That's right there in the installation instructions. It is designed so that any condensation that forms inside that pipe can flow back to the heater where it gets collected as condensate. If it is angled the other way so water flows away from the heater it will hit that cold air and freeze causing a partial or full ice blockage inside the pipe. If your exhaust is level then it was done incorrectly. It needs a slope similar to a water drain line.

    The slope needs to be 1/4" per foot of vent line. So a 40 foot vent needs the exhaust point to be 10 inches higher than the pipe where it turns into the heater to comply. The slope must also be continuous. No section of the pipe can dip and then go back up higher or you will create a pocket for water to sit in also blocking the line.

    Check for debris in the lines. The intake could possibly suck in some debris. Rodents have been known to try and build a nest in the nice warm exhaust lines if the cap is missing or if they can chew through it. If a blockage is suspected you might have to push an inspection camera into the line to verify.

    1. Thanks, Mike. Pretty sure this is the problem.

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