Hot water in cold line

[Monguila]

Hello. Looking for advise on this issue.

When I first moved to this house 10 years ago, I installed a recirculating pump on the hot tank, with a valve at the furthers sink. I remember the plumber saying that I would get some initial hot water in the cold line, when using a sink. And I did. The plumber did not install a check valve.

Fast forward to 2021. A Navien NPE210A was installed (see attached picture) with the NaviCirc valve installed at the furthers sink since there is no dedicated return line. The cold line comes into the unit from the left side. The sequence is a follows: check valve, T to return inlet, small expansion tank, check valve, cold water inlet.

Unfortunately, there is still warm water in the cold line. NPE210A indicates that the IN water-temperature is in the 80s. The cold line out of the wall feels warm when the recirculating pump is running. Warm water is coming out on the cold side at the sinks when the pump is running. There is an outside bibb that is particularly warm. It is in the middle of the house, closest to the middle bathroom.

The two bathrooms and kitchen have been remodeled since I moved in. This includes new water fixtures and valves all around. There are two one-handle showers and one one-handle kitchen fixture, with a sprayer. They are all between five and 10 years old.

Your comments and advice will be greatly appreciated.

 

[Reach4]

That's the way it works. Either put in a dedicated return line, or be rid of recirculation. That said, there is a major factor in the Navicirc system that I don't understand. In some recirc systems that use the cold supply as the return, it is the under-sink device that checks the temperature to shut recirculation off. In the Navicirc I fear the temperature sensing is done at the WH, which would heat the cold supply a lot more than necessary. I don't know what the actual method is. If the sensor is at the WH, that seems like a really bad system.

https://terrylove.com/forums/index.php?threads/navien-npe-240a-with-navicirc-valves.88186/


How about running a return line with PEX through the attic? I have no relevant experience.

 

[Sponsor]

 

[Monguila]

That's the way it works. Either put in a dedicated return line, or be rid of recirculation. That said, there is a major factor in the Navicirc system that I don't understand. In some recirc systems that use the cold supply as the return, it is the under-sink device that checks the temperature to shut recirculation off. In the Navicirc I fear the temperature sensing is done at the WH, which would heat the cold supply a lot more than necessary. I don't know what the actual method is. If the sensor is at the WH, that seems like a really bad system.

https://terrylove.com/forums/index.php?threads/navien-npe-240a-with-navicirc-valves.88186/


How about running a return line with PEX through the attic? I have no relevant experience.

Thank you, Reach4. Running a dedicated return line would be very expensive as, the ceilings are vaulted and there is no attic. If it is normal for some warm water to get into the cold side, I am OK with that. I just want to ensure that there are no plumbing issues in the house. I will call Navien and ask if anything can be done.

 

[Reach4]

Thank you, Reach4. Running a dedicated return line would be very expensive as, the ceilings are vaulted and there is no attic. If it is normal for some warm water to get into the cold side, I am OK with that. I just want to ensure that there are no plumbing issues in the house. I will call Navien and ask if anything can be done.

In particular, maybe ask how to reduce the temperature at which the recirc happens. If that happened at 80 degrees instead of 95, that would be that much less heating of your cold.

It may be possible to run the the recirculation line outside through the yard. Not common.

 

[Monguila]

Thank you! I will ask. Waiting for support to pick up the phone. Yes, a line could be run outside. It would not be as clean and it would have many 90s, but it is doable.

 

[Monguila]

As you indicated, that is the nature of the beast. In retrospect, I was confused by a similar post with the same problem. However, that application had a dedicated return line, unlike my application. Thank you again!

 

[Jadnashua]

With my recirculation system, it closes things off at about 95-degrees. I find that if I flush the toilet, it pretty much clears the line of hot. It depends on where the sensing is done, but it’s normal when you don’t have a dedicated return for the cold line to get at least warm.