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I recently had a Rheem Tankless Water Heater installed. The rtgh-95dvln-2. They installed the pump kit meant for the water heater, the ap17920. However, I do not have a dedicated recirculation line, so they used one of those under the faucet bypass valves to have the recirculation go through the cold line.

The pump gets the hot water there but the bypass valve is thermostatic and closes when it gets to temperature. The water heater keeps running the pump until the water at its inlet is 15 degrees less than its outlet set temperature. Since the valve closes, the water never makes it back to the heater and the pump stays on and gets quite hot.

I have unplugged the pump because I think its not good for the pump to run without any flow. I am trying to find the best solution. I believe my options are:

  1. Run a dedicated line for recirculation. However, I have a finished basement and its really not even realistic unless I remove a considerable amount of drywall. I could perhaps get a line halfway there (to the kitchen) but I was hoping to get hot water to the far bathrooms. Could I have a dedicated line and the bypass valve?

  2. Re-wire the pump to use a timer. I was thinking a smart-home timer so I can set it on for a minute or two, then off every half hour or so. I'm hoping with such a small interval, the pump will not overheat.

  3. Replace the pump with an ECM pump? I have been told that these are variable speed pumps and if there is no-flow, they will simply shut off. Any suggestions for one? The current pump has a flange and a drop in replacement would be nice.

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  • Tankless use massive amounts of power to heat the water quickly. putting a recirculating system on a tankless sounds really silly to me. if you want instant hot water add a small point of use tankless close to where you want it will heat the water until the main units hot water gets there. I have had to add point of use for some homes because the home owner wanted hotter water than even a very large unit could supply at the flow wanted.
    – Ed Beal
    Sep 24, 2019 at 14:06
  • This is a natural gas tankless water heater, not electric.
    – Kreuzade
    Sep 24, 2019 at 14:08
  • I have added electric point of use even on gas. The amount of gas or power either unit uses is huge you loose any gains that a tankless would provide is the point I was making.
    – Ed Beal
    Sep 24, 2019 at 14:37

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