A while ago we had a plumber/friend install a Navien tankless water heater. We trusted him and thought everything was just fine as we were getting hot water throughout the house. There is a circulator pump, but it still takes a long time for hot water to reach the upstairs bathrooms. Also, as I'm taking a closer look at it, I'm concerned that some key things may be amiss.

  • The cold water pipe coming from the wall goes into the domestic water inlet on the tankless heater, as it should. However, the plumber branched this off into the circulation water inlet. Is this correct for the function of the system?

  • When attempting a flush of the system, I shut off the hot and cold valves that lead into the heater. When I hooked hoses to the service pipes, the system still produced a strong, steady flow of water, seeming to not drain. This made me suspicious that water was coming from the mains. Is there a way to tell if the cold pipe is circulatory/return line or cold water from the mains?

  • You will see in the photo that the cold water valve enter image description hereshuts off water into the domestic water inlet but doesn't have a shut off into the circulation water inlet. Therefore, I can't drain the system. Is this incorrectly installed?

  • Any tips on where to verify if I have a dedicated return line? House was built in late 1990s and is 2 story, built on a slab foundation.

I'm fairly handy with DIY plumbing, but not and expert and I know when I am out of my league. If pointed in the right direction, though, I might be able to solve this. I would appreciate any help and insight you can offer.

3 Answers 3


That installation is incorrect. You can tell because the cold supply line is connected to the circulating return. The circulation return needs to come from a loop at an end of the hot supply line.

The user manual for these devices (of which I own two) provides a pretty good plumbing diagram for proper install. Consider yourself lucky if this installation hasn't damaged your circulating pump inside the unit.

  • Thanks for confirming and letting me know about the potential damage to the circulating pump as that hadn't occurred to me. I agree the user manuals are very helpful. I may be able to correct this if I solve the mystery on where the dedicated return line might be. Any thoughts on that? Oct 27, 2019 at 15:00

Actually the only real issue is the lack of isolation valve on the recirculation connection, resulting in the constant water supply to the water heater. Depending on the age of your Navien NPE-A model, he did you a favor. You need a crossover valve installed under one of your faucets that is far away from the water heater (there are a few different styles but they all have four connections and get installed under a faucet). Also the unit needs to be set to utilize the recirculation feature. It's unfortunate he's not around to explain all this to you. If enabled you would find that your hot water is ready to go almost anytime you need it, without a long wait. Most of information is available in the install manual but some of it requires a phone call to Navien support. Also you need not be concerned about pump damage. That install is exactly as specified in the newer manuals. Perhaps not everyone is familiar with the newer manual.


The only problem you have is there is no check valves in place check valves or like stop signs that direct traffic check valves, direct to flow of water. You need a check valve on the cold inlet 3/4 pipe also from the looks of the picture, you do not have a true designated recirculation line from your furnace fixture. All you have is a crossover valve underneath a sink somewhere also when plumbed correctly, all of that will only function with proper dip switch settings, perimeter settings, which is Pacific per heater model

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