Navien 240A, Warm Shower at Times

[JojoM]

Internet search led me to this forum and a few posts about what I'm currently experiencing. I had a Navien 240A installed about 2 weeks ago. I have a PEX recirculation line that goes from my unit to the copper pipe to my kitchen sink hot line.

Every once in a while when taking a shower the water goes from hot to warm and stays on the warmer side. I was not sure if this was normal for a tankless so we basically thought we would have to live with it. Once I found this forum I know this is not normal.

I opened the panel and confirmed that the unit is set to ext recirculation, DIP 1 of off and 2 is on. Tonight when I get home I'm going to set it for internal recirculation and set DIP 1 to on and 2 to off. If that fixes the problem I will know its probably the ext recirculation line that is the problem.

Sorry that this is so wordy but here's my questions. I have a shut off on the PEX line but no check valve, so if putting a check valve in will help my issue where do I put it? By the unit or the Tee of the copper line. Since its a PEX line can I just use a shark bite check valve. And if I just decide to stay in internal rec mode and bypass the rec line, what happens to the water just sitting in the line?

Thanks

 

[Fitter30]

Was the internal/ external valve in the correct position? Lower left in heater.

 

[Sponsor]

 

[JojoM]

Was the internal/ external valve in the correct position? Lower left in heater.

Yes it is set for external and dip 2 is on

 

[Bannerman]

I have a shut off on the pex line but no check valve, so if putting a check valve in will help my issue where do I put it?

One thing you might try is keeping the settings in External mode and run a Hot shower similar as you would while actually showering.

Once the shower temp becomes only warm, while the shower continues running, immediately shut off the valve on the return line to determine if the shower temp will become hot again. Shutting the valve will temporarily act similar to a check valve on the return line as water in the return line will be prevented from flowing in reverse to the shower.

If recirculation line backflow is the cause of the issue, the shower temp may take some time to become hot again, depending on the piping distance between the return loop connection (kitchen) and the shower control.

Have you checked to determine if the temp at the kitchen faucet is also only warm at the same time the shower is only warm?

 

[JojoM]

One thing you might try is keeping the settings in External mode and run a Hot shower similar as you would while actually showering.

Once the shower temp becomes only warm, while the shower continues running, immediately shut off the valve on the return line to determine if the shower temp will become hot again. Shutting the valve will temporarily act similar to a check valve on the return line as water in the return line will be prevented from flowing in reverse to the shower.

If recirculation line backflow is the cause of the issue, the shower temp may take some time to become hot again, depending on the piping distance between the return loop connection (kitchen) and the shower control.

Have you checked to determine if the temp at the kitchen faucet is also only warm at the same time the shower is only warm?

I didn’t even think to test the kitchen, mostly because I was actually in the shower when it happened. However thanks to your advice I’m going to run the shower and if it goes warm then I will check the sink. And when you say shut off the valve on the return line do you mean my PEX recirculation line? I will try that option as well.
Thank You

 

[Bannerman]

From your initial description, it sounds as though the home's supply lines are copper and only the recirculation return line is PEX. You said there is a shutoff valve on the PEX line so that will be the one to close.

... going to run the shower and if it goes warm then ...

Does this issue consistently occur or is it only occasional?

 

[JojoM]

From your initial description, it sounds as though the home's supply lines are copper and only the recirculation return line is PEX. You said there is a shutoff valve on the PEX line so that will be the one to close.


Does this issue consistently occur or is it only occasional?

Yes the houses main lines are all copper. And I have a single PEX line that they just ran from the unit to the sink hotline and Tee’d into that for the recirculation line. That does have a shut off for maintenance but no check valve.
It does not happen every time, I’d say it’s only been three or four times in the two weeks we’ve had the unit, so originally I wasn’t sure if it was just some thing that was normal.

 

[Bannerman]

Navien doe not specify a check-valve is necessary, but I prefer one to be placed where the return line is Tee'd into the supply line, which should then ensure 0 water will back feed to the fixtures.

If you view the External Recirculation Mode diagram that Terry inserted into post #4 above, you will see an additional check-valve should not be necessary as the check-valve Navien included to the right of the Circulation pump, should prevent backflow into the Recirculation Water Supply (return line) even while the pump is shut down. Unfortunately, that Navien check valve has been less than reliable as it will often allow Cold incoming water to flow to the left and mix with the outflowing hot water when there is no external circulation loop (Internal Recirculation mode diagram). Because you are using an external circulation loop, any cold water flowing in reverse through a Navien check-valve that has failed, will flow back into the recirculation return line and may result in the issue you are experiencing.

 

[JojoM]

Because you are using an external circulation loop, any cold water flowing in reverse through a Navien check-valve that has failed, will flow back into the recirculation return line and may result in the issue you are experiencing.

That actually makes perfect sense to me ,thank you. I would venture to guess that even without the external recirculation line if that check valve went bad you could experience the same issue. Probably wouldn’t hurt to have a spare one on hand just in case.

 

[JojoM]

Update: over the last few days I have run the shower a few times to recreate the water temp difference. It only happened I would say one out of 10 times where there was a noticeable difference. With the shower still running I checked the bathroom sink hot water faucet and it felt warm but not hot and the kitchen sink faucet where it was warm but not hot. Based on what you guys have said in this thread it leads me to believe that some cold water is leaking back from that check valve.
Some of the terms you guys use are a little confusing to me so I’d like to just dumb this down a bit if you don’t mind. I have a red pex line that they installed for Recirculation that connects to the rec fitting on the Navien and then is teed into the hot line of my kitchen faucet. So if I’m going to install a check valve it should be installed in the red pex line. Is this correct?
Thank you for the help

 

[Bannerman]

it should be installed in the red pex line. Is this correct?

Correct. The flow direction arrow on the check-valve will point toward the WH.

There are two main types of check-valves, swing and spring-loaded. A swing check will open easily but will only close by gravity so to close properly, it will need to be installed in a section of the recirculation return line that is horizontal. A spring-loaded check valve will require some additional pressure to open but may be mounted in any orientation. Either type will work but you should determine where you plan to locate the CV before purchase. If you plan to install in a vertical section, you will then want to ensure you do not purchase a swing version.

Did you try shutting off the valve on the return line while the water was only warm to determine if the water became hotter?

Probably wouldn’t hurt to have a spare one on hand just in case.

It sounds as though you also plan to replace the check-valve that is internal to your Navien and also plan to obtain a spare.

 

[JojoM]

Damm, I was so excited thinking the check valve was the solution to my problem that it never occurred to me to continue testing with the pex line off .

 

[Bannerman]

It's possible although unlikely the thermostat control for your Navien is the cause of the problem. Always best to test various possibilities before deciding the cause.

Shutting off the valve on the return line should confirm if it is a backflow issue as the temperature should not increase if the thermostat was the cause.

I said the thermostat is unlikely as the water is first fully the temperature you have set and then becomes cooler with use which, unless you are using hot water faster than can be heated by a NPE-240A, is a usual indication the check-valve is defective.