My house currently has a hot water recirculation system, but it does not seem to be functioning as the water in the upper levels take minutes to get warm.

First off, I tried to determine whether I had a dedicated return line for recirculation. The piping around the water heater was quite complicated and I could not figure out what goes where, so instead I opted to look under the all the sinks in the house to determine if there was a temperature valve. Having seen none, I deduced that we had a dedicated recirculation line.

At this point I'm not sure how to proceed. The pump appears to be working. When plugged in, it hums along and I can feel the flow of water along the lines. Unfortunately, the water heater does not turn on at all when the pump is on, and there is no noticeable difference in the time it takes for hot water to reach the sinks in the furthest fixtures.

I've attached pictures of the piping around the water heater + pump for clarity.

Edit: I've removed the insulation on the pipes in the pictures for more clarity.

The pump model is Grundfos UP26-96BF, and the RINNAI model is R94LS.

Overview of pipes Overview of pipes at different angle Pipes on top of water heater

  • what is the pump model and the RINNAI model? If the red pump is the recirc pump, it should feed into the recirc input of your heater. I can't follow the piping with the insulation over it. Is it possible to retake the pics with insulation removed?
    – P2000
    Jan 10, 2022 at 20:00
  • I have a pump like that that did not work well. Took the pump apart and found it blocked with hard water scales. Cleaned it out and work well after.
    – crip659
    Jan 10, 2022 at 20:03
  • The pump model is Grundfos UP26-96BF, and the RINNAI model is R94LS. I have also edited the original question with the pictures without the insulation on the pipes
    – Ish
    Jan 10, 2022 at 20:30
  • 1
    HW recirc doesn't play well with on demand HW heaters. Jan 11, 2022 at 5:24
  • 1
    I'm no expert, but having all that plumbing just hanging there, unsupported, especially with the expansion tank hanging off of it, just seems to be asking for soldered joints to leak.
    – FreeMan
    Jan 11, 2022 at 14:19

2 Answers 2


Your RINNAI does not have a recirculation input. The manual mentions two setups of which the following is I believe yours:

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Thank you for the pictures without insulation, but I still can't make up from this copper mikado what is going where. Hopefully you can trace it with help of the above diagram.

Your check valves (one way valves) look like this:

enter image description here

For recirculation to reach far away bathrooms, there must be a third pipe leading to that bathroom and tapping off the hot to return to your mechanical room. Recirc will only reach as far as such a tap-off. Sometimes recirc reaches the kitchen and one bathroom but perhaps not a second bathroom.

As an aside, some other brands/models of on-demand heaters do have a recirc input, generally when they have an internal recirc pump and reservoir.



  • Based on the pictures, I get the feeling that the recirculation flow never leaves the mechanical room. Nov 2, 2023 at 13:43
  • @BartvanIngenSchenau well, I think there is no recirc, see my answer
    – P2000
    Nov 10, 2023 at 5:29

Assuming the system is properly designed and was working at some point, the main suspect in recirculating systems is trapped air. Make sure that you open all faucets and appliances that use hot water until all of the air is out.

Also, just because you can feel the water circulating after the pump, it does not mean the pump is working properly. It could be clogged and/or not holding pressure. After you make sure there's no air in the pipes, try changing the pump. The cost will be less that a service call to a plumber.

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