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Navien NR-240A Troubles (Error 38)

July 5, 2013

We ran into an issue with our Navien NR-240A this weekend.  The heater has been running more-or-less smoothly for 18+ months now, and we haven’t had any major issues since the defective part that was in the device when it was installed.

Yesterday was July 4th, and we had company coming over.  A couple hours before our guests were scheduled to arrive, my wife asked me if there was a reason we didn’t have hot water.  Um, no….

I went down into the basement and checked out the Navien NR-240A.  No error messages on the thermostat, but it wasn’t running as it should have been.  So I unplugged the unit, waited a minute, and plugged it back in.  I waited a few seconds and the heater seemed to be running, so I turned on the sink.  I had warm water, but it quickly got cold.  I went back to the heater and it was now showing me a 38 error. I checked the manual and it suggested the problem had to do with water flow (check the circulation pump, check the flow sensor, check the water intake).  I was betting the problem was with the flow sensor since it seemed like the circulation system was working (albeit briefly) and I clearly had flowing water.

I called the folks that installed the water heater.  I explained the issue, and they told me that since it was a holiday and this was warranty work, they wouldn’t be able to come out until the next day, but that we would be toward the top of their list.  I said fine.  We celebrated the fourth and I just boiled some water on the stove so that I could wash the dishes.

At 10am we still hadn’t heard from the plumber, so we decided to call.  We weren’t on their list — apparently the guy I spoke to the day before didn’t call our call in.  Thanks Max.  They told us they would come out in the afternoon, and called around 1pm to say they were still going to be a while, and called again around 5pm and said they were 30 minutes away.

After working on the heater for about 2 hours, the technician (Jeff, who is the same gentleman that installed the heater and who has been great) said that he had resolved the issue.  He had done some routine maintenance (cleaning screens) and taken the flow sensor apart and cleaned it (apparently as he is required to do by Navien before replacing it) and while he found no visible issues, said that seemed to have corrected the problem.  I paid him ($200).  He left.

About ten minutes later my wife called me in and said we didn’t have hot water.  I checked the Navien, and it wasn’t showing any errors.  I called the plumber back and he was genuinely shocked.  I repeated the steps from yesterday — rebooted the heater and got the error 38 — and he got off the phone with me to call Navien to order a new flow sensor for me.

The trouble is, today is Friday and the new sensor won’t come until Monday, and there’s no indication when on Monday it will come.  So we may not have hot water until Tuesday.  Yikes.

So… For those of you out there with tankless water heaters — is this normal?  I think I can live without hot water for a few days, but $200 in maintenance after only 18 months of ownership….?  Seems kind of steep.  I’m beginning to regret having bought one of these.  Short of a normal water tank failing, I never had any problems.  And then it was a fairly straight-forward fix — i.e., I never had to go five days without hot water.


From → HVAC

  1. Malcolm permalink

    I have a similar problem with the Navien NR-210A.
    The flow sensor – a device that measures the volume of water flowing through the heater – regularly fails. The typical life of this part is 18 months to two years.
    Cleaning this part may resolve the issue – the trace amounts of fibre and grit normally present in water partially clog the device. There is a little “propeller” in the part, so it turns less easily, and thus communicates the message that the water flow is less than what it actually is. So, the heater is confused, and produces water that is warm/lukewarm, not hot.
    Replacing the part is more certain, and I hope that some day Navien will finally figure how to build a more robust version of this part.
    The same part is used in the Navien NR, NC, and C series of their tankless heaters – so the problem is likely the same for all.
    The part is easy to access and replace, but does require shutting off power and water flow (hot and cold), and draining the unit. Basic handyman skills, but not much more.
    After paying to have a plumber do it twice, I just did it myself.
    I have also heard that a light tapping on the flow sensor will sometimes dislodge the fibre/grit. As this is quick, I’ll try that the next time I encounter this problem.
    Water heaters with tanks are simpler and therefore less likely to fail. They cost more in energy, but repair costs are less frequent and costly. Don’t expect the benefits of a simple tank water heater when you get a tankless.

    • Thanks Malcolm. I’m concerned that you have had to change the flow sensor three times already. That makes me think I should order an extra one now.

      I agree that the part seems like it should be fairly easy to replace. I was unlucky in that the flow sensor in my unit failed on a holiday weekend, and so it was hard for me to get a plumber to come do the work. I managed to get someone to come out to order the part, but after the part came, I was told by the plumber that they wouldn’t be able to install it for another three days. I was at work when I was told that, and was planning on changing it myself when I got home, but the plumber ended up having an opening during the day and came and changed it for us. Which was great, but cost another $120.

  2. Currently I have the same problem. I cleaned filters and flushed the system and it worked for a couple of days. Service tech. (who had never seen a Navien) after long talk with Navien, indicated the flow sensor. This was verified with a few taps on the sensor. I am still waiting for the flow sensor, meanwhile, to get hot water, I cycle power, turn on a hot water tap and tap the flow meter to get it going again; that is until the hot water is not needed making the heater shut down. Next time hot water is needed I have to repeat the above.
    Since this flow meter seems to be unreliable, I’m ordering an additional for a backup.

  3. p shaw permalink

    It was under warranty your plumber ripped u off navien pays labor on warrantied boilers yes it is common the flow sensor opens up if u take it out and push it back together it will work navien should have sent u a new version of the flow sensor.i am a trained tech for the company

  4. Zach permalink

    I am a plumber and have installed 30+ Navien units in the Northern Nevada area for last 8 years. I have only had a small fraction of them call back for a warranty repair. It seems to me that the common denominator of the flow sensor problem is water quality. Not one of the Naviens installed on a water system with a water softener has had a problem with the flow sensor or a 38 error code. If you’re constantly dealing with a problem with a flow sensor, you may want to invest in a sediment filter (if you’re on a well) and water softener system.

    Also, Navien has always been very good at overnighting replacement/warranty parts. I always get them the next day.

    Just like any intricate piece of machinery, these tankless units require maintenance and TLC, if properly taken care of, they can save you a ton of money in heating costs.

    • Malcolm permalink

      I had the flow sensor fail again. To eliminate water quality as a source of the problem, I installed a 5 micron water filter on the cold water feed, and had the tank flushed, and had a new flow sensor installed. Reliable hot water again – for about 24 hours. Then, no error, just cold water.
      Called the plumber back – he was mystified, but it started working after draining, removing the sensor, and blowing through it. Reliable hot water again – for about 24 hours.
      My experience is the flow sensor may last up to a year, and that it usually fails in winter when the cold water becomes a few degrees colder. Not sure why – my next project is to measure the reliability of the Hall effect sensor that the flow sensor uses, at different flow rates.
      Oh, you can rotate the flow sensor internal “propeller” by unscrewing the electrical sensor from the body of the flow sensor. Tuck that bit out of the way, then pass a magnet through that slot on the flow sensor where that thingy was mounted. Screw the wired piece back in place – no draining required, no plumbing disassembly.
      But, unless you are willing to add a hot water heater to your list of high maintenance appliances, I’d keep away from these things, and go for the low tech old fashioned tank heater.

  5. Sharon Finley permalink

    ICE COLD SHOWERS are what I get with my Navien NCB-240!!!! It is supposed to handle both the radiant floors and the domestic hot water. The poor plumber was out at least 6 times the first winter and replaced everything there was to replace on the unit and tested it numerous times while talking to the Navien engineer. I got one more cold shower and then turned the heat off for the summer. Had the same problem again as soon as I turn the heat on again for this winter.
    I am no longer under the 1 yr. contractor guarantee. When I called to complain to Navien, they said they would only work with a plumber. I called the one they recommended and Washington Energy. No one would touch the problem. Finally 1-800-Contractor made someone come out. Last year Navien said I was the only one having this problem, this year they say the system is working as designed. I get the normal cool water which turns warm when the little bit of water in the tankless reaches it, then it turns cool again and gradually warms and then turns hot just long enough to get my hair soaped up, then it turns ice cold for almost exactly 3 minutes before turning hot again. Now it turns icy multiple times. None of the hot cycles are long enough for a 3 minute shower. Four of us shower, using 3 different showers, early in the morning which is also when the radiant floors are heating up. We all get cold showers and waste a lot of water. Two of us now sick with a miserable cold.
    The plumber said I can’t even add a regular gas hot water tank for my domestic hot water because of the venting system. I can add another Navien tankless but that is expensive. The plumber explained my many service calls and how unhappy I was but Navien would not even offer me a price break on the 2nd heater. I would not recommend this unit to anyone.

  6. Cameron Babcock permalink

    E38 and now water flow is the 2 way valve un plug the three wire plug on the right hand side of the board that is label “way” blue yellow and orange wires

  7. Micheal Duff permalink

    I think my problem is similarly connected to the flow sensor. My problem is that the GFI switch in the unit keeps tripping. Sometimes immediately, sometimes after 5 minutes. This is all new, as we had no problems like this until about a week ago. I reset the switch and it worked for a few days, then it started tripping more often. Thanksgiving weekend here in Canada, so nobody available to troubleshoot it for me, and woke up to 6″ snow this morning, and no hot water to warm up with a hot shower….

  8. NoHotwater permalink

    I have NPE-240A and I am experiencing the same issue. Error 438. And than the whole units trip the circuit. leaving us with cold water. I called customer service and they told me to disable the circulation pump by changing the first Dip-Switch on left side. They wouldn’t send the flow sensor (though still in warranty ) without Plumber’s diagnosis. I am not willing to spend hundreds of $$ on an issue that can be DIY job. Navien should acknowledge this issue, put a video as to how to replace this flow sensor and at-least should provide this for free during 5 year warranty period. My unit was installed in April 2015, it is just close to 3 years, before it gave up. I am running the unit without the circulation pump now till I figure out how to get this fixed.

    • I was able to purchase a new flow sensor from a third-party for less than $50, if I recall. I found, though, that the problem was with the circulating pump, and I decided not to replace it because we didn’t really “need” it and the job was bigger than I wanted to bite off at the time. If I recall, the circulating pump was about $250 from third-party sites.

      Good luck!

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