Navien - hot water coming out the cold inlet

[Jon Austin]

I have a Navien NR-210A - about ten years old and recently, in external circulation mode, its sending hot water out of the cold inlet when it recirculates. There is a dedicated recirculation line and external circulation has worked well for for those ten years until now. There are no issues with recirculation turned off or when in internal recirculation mode.

Any ideas on the most likely part causing the issue? Is there a way to test if the 3-way valve is faulty before replacing?

Thanks for any ideas.

 

[Bannerman]

The 3-way valve controls the feed source to the pump inlet so it has no effect on flow direction after the pump.

As hot water is exiting the cold inlet, where is it flowing to? Water will always follow the path of least resistance. For hot water to exit the inlet, it will be pushing against and will need to overcome the pressure from the water source.

The path of least resistance should be though the home's hot water distribution lines to where they connect to the return line back to the WH. Are there any valves in the recirculation lines which had been open but are now closed? If there are check valves installed, verify they are allowing water to flow through.

If water can't enter the WH through the supply line, there should be no other source for additional water so water should not be flowing out. Is there another location within the home where water could be entering the hot water system such as a kitchen or laundry faucet equipped with a handheld sprayer control, or a valve on the end of the faucet spout where the hot and cold faucet controls remain open while not in use?

Another possibility is a shower equipped with a valve on the shower arm or handled showerhead which is being used to shut off water flow while the main control valve remains open?

A further possibility is a 'Y' type flexible hose supplying a mixture of hot and cold water to an appliance?

A simple method to prevent water from flowing in reverse out the WH supply line would be to install a spring-type check valve in the supply line below the WH. Unfortunately, that will not explain why a check valve is now suddenly needed when no check valve was needed for the past 10-years.

 

[Sponsor]

 

[Jon Austin]

Thanks Bannerman, you're right it seems the culprit is actually some sort of cross over at the shower. The recirculation line meets the hot water at that point, so I think that is why I only noticed it when external circulation was running and hadn't noticed that hot and cold water were meeting there.

I'm not sure yet if there is a faulty crossover valve or whether I can access it without going through the wall. Are there any potential problems with just installing a check valve in the basement below the shower to prevent water flowing back up the cold water line?

 

[Bannerman]

not sure yet if there is a faulty crossover valve

You said there is a dedicated return line so a crossover valve should not be utilized. Normally, a check valve will be utilized in the return line to prevent water in the return line from flowing in reverse to the running shower or open faucet.

While a single check valve can be installed anywhere in the return line when there is a single return loop, if there are multiple return loop branches which combine prior to the WH, then each branch will require its own check valve. Suggest using spring check valves as each may be installed in any orientation, unlike swing checks which must be installed only in a horizontal plumbing line.

 

[WorthFlorida]

I have a Navien NR-210A - about ten years old and recently, in external circulation mode, its sending hot water out of the cold inlet when it recirculates. ....

Lately there seems to be a rise in complaints with this type of problem. As more units are installed and aging, problems are bound to come up. I agree that there is a crossover occuring and to find the location is fairly easy. Close all stop valves both hot and cold at every fixture including the clothes washer except the fixture closest to the WH. Then set up your circulation mode to cause the problem. If everything is normal at this fixture then open the next fixture, test then the next and so on. If the problem was at the first fixture I would suspect something at the Navien.

Keep testing until the cold water is warm or hot and that is the location of the problem.
Installing a check valve at the shower is only a patch and not a fix.

Something is stuck open and if you have any crossover valves (doubtful because of a dedicated return line), they can get jammed open due to mineral deposits or if it is spring loaded, the spring broke. 10 years is a good amount of time with no problems so the problem is not with the install but a component.

 

[WorthFlorida]

Let me retract a bit. If your return line is at the furthest fixture as shown below, start the testing there. Do not close the the last fixture.

 

[Jon Austin]

Let me retract a bit. If your return line is at the furthest fixture as shown below, start the testing there. Do not close the the last fixture.

Thanks all. I replaced the shower cartridge and that solved the problem.