Navien 240A not getting generating very hot water

[kwolfe19]

I'm trying to diagnose what is going on with my Navien 240A hot water heater running on natural gas. We've had it for about 6 years, and it's worked fine up until now. It gets descaled each year with vinegar and the filters get cleaned (air and cold water intake).

Yesterday my family complained that their showers were not very hot. This morning I had a similar problem, water was warm, but not hot. It started out hot, but then got cooler. There are no error code. When looking at the unit and stepping though the various informational codes, a few things seem odd. One the GPM rate for 'A' seems low. When I have a shower on, full hot, it shows .6GPM, same with the kitchen sink. Also, the flame indicator is not coming on immediately after I turn on the water (and that's after I walk from the kitchen into the garage). Also, sometimes the flame indicator goes off while the water is running on full hot. The second thing is that the the value of 'B' isn't 120 (which is where we've got the hot water heater set to). It was 118, and sometimes would go lower to like 110.

Any ideas how to troubleshoot further? I was thinking this was a flow sensor issue, but after doing more research, I'm not convinced I know enough to diagnose. Also, Navien help was not super helpful. They just said to call one of their installers. If it's something simple to replace, I'd rather do it myself and save some bucks.

Thanks!

 

[Bannerman]

This is a common problem caused by the internal check valve not fully closing as it should which is allowing some cold water to flow directly to the hot water supply connection backwards through the circulation pump. Since that cold water is not flowing through the flow sensor, the flow rate indicated is less than expected.

Replacing the check valve is the usual remidy, and you did well with no issue in 6 years use. While a few forum posters have had some success in removing and cleaning the exsisting check valve, the same problem will reoccur. It is an inexpensive component and is easy and quick to replace yourself. Even if you attempt to clean and reinstall the exsisting, suggest buying at least one replacement so you will have another on hand to swap in when the same issue occurs again.

 

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[kwolfe19]

Thank you for your reply. Earlier today I ordered 1 flow sensor and 2 check valves. They’ll show up tomorrow. I’ll try to replace the check valve first and hopefully that will do the trick. Then I’ll have the other items in reserve. I hope it works!

 

[kwolfe19]

So I replaced the check valve and everything is working great now. Super easy fix, took about 15 minutes total and that was with explaining to my kid what I was doing.

In terms of diagnosing the problem, I thought I'd leave this here for others in case my explanation is helpful.

To figure out that the problem is the check valve, you need to make it so that the cold water cannot flow backwards through the check valve into your hot water supply. For me, that meant changing the dip switches to have no recirculation (switches 1 and 2 in the off position) and setting the valve that controls internal vs. external recirculation to external and closing the external circulation valve on the pipe that goes to the recirculation pipe circuit. Then if you turn on the hot water at a tap, you should get nice hot water and not have the water get cooler.

 

[Bannerman]

The purpose of the pump being active while the 2-way valve is in the Internal position is to periodically circulate water from the buffer tank through the heat exchangers so as to maintain the temperature of the water within the buffer tank.

Turning off the pump control switch and placing the 2-way to the External position, will not allow any circulation so the water within the buffer tank will cool off when no hot water has been drawn for several hours and will result in longer time for hot water to arrive at home fixtures.

 

[kwolfe19]

My suggestion was not meant to be a permanent one, more of a test to see if swapping out the check valve will be likely to fix the problem. Also, even though you can/will end up with "cold water sandwich" behavior in this mode, at least your shower will be hot while you wait for your replacement part to arrive!

 

[Bannerman]

There will be someone that reads this in the future that will consider your instructions to be a permanent fix, but will then complain that it is taking too long for hot water to arrive to fixtures.

 

[cscotta]

@Bannerman and @kwolfe19, thank you for this thread!

I've had exactly the same problem with my NPE-210A2 at just 18 months old. Lukewarm water from taps open for 5+ minutes, a low egress temp reported by the unit, and a lower than expected flow rate appearing on the unit's display - resolving immediately if an additional tap is opened, increasing the flow rate.

The installer refused to answer or reply after performing a standard cleaning that didn't resolve the issue. Your posts here helped me diagnose the problem, and the temporary workaround brought reliable hot water for family visiting during the holidays.

Flipping the recirculation valve to "external" and disabling recirc in the unit's settings results in the WH producing hot water again – albeit with the delay you warned about. A replacement 30024442A check valve is in the mail and should be here for me to install later this week.

Really appreciate your clear description of the issue and background on the internals. It gave me the confidence needed to fix it myself.

Thanks again and happy new year from San Francisco.

 

[cceddie95]

Experiencing the same issue, unit is almost 6 years old. I've descaled and replaced flow sensor already but that didn't seem to last very long. I do not have any external recirc setup and noticed that the installer set the 2-way valve to Internal but all the dip switches are off. Has this been setup incorrectly the entire time? After reading this thread, I'm thinking the check valve make the most sense as next step considering we have very hard water. Navien tech support was down right rude, wouldn't even answer a question and just kept replying with "you need to call a licensed plumber."

 

[cceddie95]

Experiencing the same issue, unit is almost 6 years old. I've descaled and replaced flow sensor already but that didn't seem to last very long. I do not have any external recirc setup and noticed that the installer set the 2-way valve to Internal but all the dip switches are off. Has this been setup incorrectly the entire time? After reading this thread, I'm thinking the check valve make the most sense as next step considering we have very hard water. Navien tech support was down right rude, wouldn't even answer a question and just kept replying with "you need to call a licensed plumber."

UPDATE: I've replaced the check valve, flow sensor, and descaled the unit again. Still experiencing water getting cold intermittently, no error codes. Problem is not limited to one faucet or bathroom. The house only has 2.5 baths, dishwasher, laundry room, all fixtures are low flow. I have noticed that it gets worse when a second water source is turned on. Unit is 6 years old, I've descaled it and done annual maintenance every year. In the past, the loss of water pressure only happened if 3 water sources were opened but water never changed temperature. Recently, both the water pressure and temp drop especially if one shower is on and someone uses the kitchen sink or turns the washing machine on. Not sure what else needs to be replaced to resolve this issue. Been very happy with out Navien 240A (natural gas) until now. Any suggestions would be greatly appreciated!

 

[GReynolds929]

What is the out temp of the heater when the temperature is fluctuating. What is the incoming water temperature. What happens if the two way valve is set to external?

 

[StanJD]

Same problem here with NPE-240A. Starts off hot (but not hot enough), then drops to about 100. Descaled and replaced the flow sensor, but no change. No recirculation line. Check valve is my next target, but trying to confirm whether it's the problem.

Video of out temp https://photos.app.goo.gl/bb4NY9eWvsUbkPEZ6

Also, recirculation valve appears leaking, red cap on the inside gets forced off.

 

[GReynolds929]

Set the 2-way valve to external and see if that solves it if it does the check valve is bad. The red cap is the pump air separator it needs to be replaced.

 

[cceddie95]

Follow up...Finally resolved temperature fluctuation issue by replacing the the Ignitor and Flame Rod.