Condo Plumbing Puzzles - Two Hot Water Lines to Shower

cj5

Hi All,

I've been trying to figure out a plumbing puzzle at my mother-in-laws condo.

There are two oddities:

1. Only hot water comes out of her shower. I've inspected the valve and can confirm the hot water is plumbed to the Navien hot water heater. The cold water is plumbed to some other hot water source possibly from another unit in the building. I used the shower valve shutoff screws to confirm this. So no cold water comes out of the shower. That shower was redone about 10 years ago but is the guest shower so hasn't been much of an issue.
2. The Navien water heater was installed a few years ago and has a water recirculation line connected to a cast iron pipe. Because of the old construction it wouldn't have a separate recirculation line so I went looking for the Navi-circ valve, that would temporarily reuse the cold water line, but I couldn't find it. So I have no idea what that recirculation line is connected to. Perhaps the installation of the Navien made the shower situation worse but the historical experience with it is unclear since it is the guest shower.

All the sink faucets in the condo unit work fine with hot and cold water.

So it would seem the shower is connected to some other units hot water line, but with the confusing recirc line situation, perhaps there is a compounding issue.

Any thoughts for how I can figure out these puzzles and fix them?

Thanks

bjohnhy

I suspect one of the lines is intended for a dedicated recirculation line. Seems like you have thought about that already. A schematic and or photos of what you know and can can confirm may help sort it out.