Navien NPE 240A2 Intermittent Low flow

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Grhoch

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Hi, I have been struggling to the past few weeks with intermittent problems of hot water dropout on a 4 month old Navien NPE240A2 system.

Setup:
NPE 240A2 installed on exterior of home. External recirculation activated with dedicated return line using built in pump.
3 showers:
#1 (Hans-grohe thermostatic, 1.9 GPM shower head) within 20 feet of heater.
#2 (California faucets, thermostatic, 2.5 GPM shower head) about 50 feet pipe length from heater.
#3 (primary master bath shower, Hans-Grohe pressure balanced, 2.5 GPM shower head) about 80 feet from heater.

Problem:
Everything seemed to be working fine for 4 months, with occasional slight temperature fluctuations in the #3 shower, but nothing that would affect usability. But then in the past two weeks we started to experience the water turning lukewarm in the middle of a shower. This would sometimes improve if you turn the water off and immediately turn it back on, sometimes it would not improve with this maneuver. I also noticed during this time that the water heater would show a flow of only 0.8 GPM when shower #3 was on, even when the temperature was set to maximum. The flow from shower #2 was 1.6 GPM, slightly better, but still not near 2.5 GPM capacity of shower head in that bathroom. The flow from shower #1 was 1.0 GPM rather than the max of the head of 1.9.

I Called the plumbing company who installed the heater and they came out and did some tests. They checked my water inlet filter and said it was quite dirty which was likely due to the recent addition of bathroom #1 and new pipes being placed in that part of the house. They also ran some tests on my shower and said my cartridge in shower #3, the master bath, was somewhat faulty and should be replaced. Initially for about 24 hours it seemed that the problem was fixed by cleaning the filter alone, but then it started to recur, so I changed the cartridge with a brand new one. This did not fix the problem. So I called the plumber back. This time they got on the phone with Navien support. The first step they had us do was check the water pressure to the house. It was 40 PSI. They said that was very low and likely the root of all the problems I have been experiencing. They were not willing to run additional tests until I rectified this issue. This didn't really make sense because the heater worked just fine for 4 months. I called the city, and a very funny coincidence, the water main down the street from me happened to have a break that same morning we were troubleshooting. After it was fixed, I checked the pressure again, and it was up to 43 PSI. I spoke to the city and they said according to their survey book, my street has pressures ranging from 45-50 PSI at the hydrants, so the 43 PSI is not that far off. After the pressure was increased to 43 PSI, I checked the showers again and the flow seemed a bit better! I was getting 1.3 GPM from shower #3 instead of the prior 0.8. 2.2 from shower #2 instead of prior 1.6, and 1.3 from shower #1 instead of 1.0. Indeed shower #3 was now useable. It remained usable for 2 or 3 days, then again started to get lukewarm in the middle of the shower and indeed, the flow as down to 0.8 GPM again.

But the problem was intermittent. If you turn the shower off then turn it back on right away, it is hot again. I ran some more tests myself. I turned shower number #3 on max heat and the heater displayed 1.3 GPM, I kept the shower on, then I ran another faucet in the house, the total went up to 2.2 GPM, then after turning off the faucet, it went down to 0.8 GPM and would not come back up to 1.3 again. I turned the faucet on again and off again and this time the shower stayed at 1.3.

So in summary, I am getting lower than expected flow to all my showers, with the worst being the one furthest away from the heater, and the amount of flow to the furthest shower varies unpredictably between 0.8 GPM and 1.3 GPM. When it drops to 0.8 GPM the shower feels lukewarm. At 1.3 it is useable.

Questions:
1) Could this all be my lower than average water pressure of 43 PSI to the house? This might explain the greater reduction in flow to the furthest shower, but how does it explain the intermittent fluctuation in flow. Also, I assume the pressure to my house was no different when the system was installed 4 months ago and I didn't notice this problem.
2) Are pressure balanced shower cartridges more sensitive to lower hot water pressure than thermostatic ones? This could explain why shower #3 is worse than the others.
3) Could this be due to the Navien flow sensor? The plumber and Navien support said this was unlikely, because there is no error code and the heater is being triggered to run just fine. To me, a malfunctioning flow sensor would seem like a good explanation, but I'm not a plumber.
4) Is the recirculation line supposed to feel cold when the hot water is currently running through a fixture? When you feel the return line out by the water heater as it exits the house, it is quite cold and you can feel cold water flowing through it as the heater is running delivering hot water to the house.
From my online reading, I thought this could mean the check valve was malfunctioning, but the plumber said the check valve was not the problem because the output from the heater remained at 120 degrees the whole time.

Here is a video of the fluctuation in flow I am describing:
https://youtu.be/x4ARWRt-ucU

Any help would be greatly appreciated as my plumber seems stumped.
 
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WorthFlorida

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So in summary, I am getting lower than expected flow to all my showers, with the worst being the one furthest away from the heater, and the amount of flow to the furthest shower varies unpredictably between 0.8 GPM and 1.3 GPM. When it drops to 0.8 GPM the shower feels lukewarm. At 1.3 it is useable.

From my online reading, I thought this could mean the check valve was malfunctioning, but the plumber said the check valve was not the problem because the output from the heater remained at 120 degrees the whole time.

The check valve could be the problem. When the shower temperature is lukewarm, what is the temperature at the output on that display? I believe the plumber stated 120º. I do not think the re-circulator affects the output temp.

With the the filter having debris and the main pipe break, sediment could be fowling up the check valve. Is the cold water filter?

I'm no plumber and never worked on a NAVIN but spent nearly forty year troubleshooting telephone problems. It's all the same to me. Eliminate and isolate. You did good on your explanation and techniques.
 

Grhoch

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The check valve could be the problem. When the shower temperature is lukewarm, what is the temperature at the output on that display? I believe the plumber stated 120º. I do not think the re-circulator affects the output temp.

With the the filter having debris and the main pipe break, sediment could be fowling up the check valve. Is the cold water filter?

I'm no plumber and never worked on a NAVIN but spent nearly forty year troubleshooting telephone problems. It's all the same to me. Eliminate and isolate. You did good on your explanation and techniques.
Update. The problem was indeed the check valve. The first guy from the plumbing company was clueless and misdiagnosed it leading me down a rabbit hole. I made them send a different guy and asked him why the return line was so cold when the water heater was running and he instantly knew the cold water was flowing in the wrong direction through the return line because of a broken check valve. The reason the master shower was most affected is because it is at the end of the hot water line where the return line connects, so after about 90 seconds the retrograde flow of cold water would reach the shower and cause it to become lukewarm. He replaced the check valve and also installed another in line check valve on the return line near the water heater as backup. Problem solved! I even asked the first plumber immediately if this was the problem since it seems quite commonly described on this forum, but he still couldn't get it right. Oh Well!
 

Breplum

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A all too common problem with the earlier NPE A models is a check valve that hangs, and symptoms are fluctuating temps.
I have yet to have my hands on this next gen A2 series check valve. But it is early in lifecycle.
Navien never acknowledged the continued check valve failures to us in the field.
 
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GinoDivx

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I just had the same model installed (NPE-240A2), and have a similar but a different problem. Should I start a new thread? My issue is that shower in main bathroom seems to have colder water than when I had regular water heater. But more importantly, when someone turns on a faucet or another shower nearby, the water becomes even colder. Not totally cold, still warm, but not hot for example. I have a separate return line, seems to be connected properly, the line is hot, and hot water is available almost immediately everywhere. Please let me know if I need a new thread. I called Navien, and they suggested to flush the heater (which was just installed last week), with contractor present, and call them, to possibly diagnose check valve. GPM was ~4.2GPM when I checked. Can check valve or something else be a problem with brand new heater? Thanks!
 

IrritatedJones

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I've had almost the exact same problem you've described as well. We completely refurbished a home. So I have brand new lines and a dedicated recirculation line. Navien NPE-240A2 was installed on Spring Break of this year. Everything worked great till late August, and then we started having some of the issues that you've described. Inconsistent hot water in all showers and faucets. Turning the hot water off and back on again fixes the issue for a few minutes and then it happens again. We have a double shower in our master bathroom, and we can have 1 shower head on and it works well. Starts out as scalding hot, and if you turn on the second one the first one will go to hot, but the second will never be hot enough to shower in and will eventually go cold. If you turn both showers on at the same time they will both be scalding hot, but after a few minutes will start producing inconsistent hot water, back to the top description. I've had the plumber out a couple times. And I've spoken with Navien tech as well. At this point, I've replaced the flow sensor, and yesterday I flushed the system and clean all the filters. Still having the same issue. Is it worth replacing the check valve at this point? Kind of frustrating because Navien won't warranty any of the parts on it if I do it myself, but waiting for a plumber to come out is getting frustrating as well. Any advice would be super helpful.
 

Breplum

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IrritatedJones, yes the check valve should definitely be replaced. On Nov. 1, 2022 Navien upped the labor reimbursement rate for models that are covered by the first year part of the warranty, so, that it is now slightly more rewarding to make those service calls.
 

Grhoch

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I've had almost the exact same problem you've described as well. We completely refurbished a home. So I have brand new lines and a dedicated recirculation line. Navien NPE-240A2 was installed on Spring Break of this year. Everything worked great till late August, and then we started having some of the issues that you've described. Inconsistent hot water in all showers and faucets. Turning the hot water off and back on again fixes the issue for a few minutes and then it happens again. We have a double shower in our master bathroom, and we can have 1 shower head on and it works well. Starts out as scalding hot, and if you turn on the second one the first one will go to hot, but the second will never be hot enough to shower in and will eventually go cold. If you turn both showers on at the same time they will both be scalding hot, but after a few minutes will start producing inconsistent hot water, back to the top description. I've had the plumber out a couple times. And I've spoken with Navien tech as well. At this point, I've replaced the flow sensor, and yesterday I flushed the system and clean all the filters. Still having the same issue. Is it worth replacing the check valve at this point? Kind of frustrating because Navien won't warranty any of the parts on it if I do it myself, but waiting for a plumber to come out is getting frustrating as well. Any advice would be super helpful.
Are you able to touch the recirc line as it enters the water heater? If so, turn on the hot water at your shower then go feel the recirc line . If it is very cold this suggests that the cold water is flowing backwards through the recirc line due to a faulty check valve.
 

IrritatedJones

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Are you able to touch the recirc line as it enters the water heater? If so, turn on the hot water at your shower then go feel the recirc line . If it is very cold this suggests that the cold water is flowing backwards through the recirc line due to a faulty check valve.
Yes, I actually went back and checked it today after rereading your post. And it is cold, like ice cold at this point. Went yesterday to get a new check valve, because I figured what's the big deal it's only a 5.00 part at most. None to be had at any of the large plumbing warehouses in the city so they ordered me one. Hoping they got the correct part number. Came home and thought it was worth pulling the it out and looking at it. Looks like the O-Ring has warped or expanded and it's causing it to get stuck and not function correctly. Guess I'll find out for sure mid-week once they get the new one in at the warehouse.
 

IrritatedJones

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Thought I would give any future finders of this thread an update. Got the check valve in after the local plumbing supply house ordered it. Switched them out and works perfect again. Super glad I found this forum and specifically Grhoch's post.
 
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