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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.

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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? – andyseven21 Oct 27 '19 at 15:00

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