Lukewarm Hot Water with Recirculation Pump On

[Deleted User]

I recently moved into a new house which has a recirculation pump and a dedicated return line. As far as I can tell, the pump is running continuously. Whenever a faucet is turned on, we have instant hot water, so everything seems to be working.

However, when we run the hot water for, say, 5 minutes in the shower, the hot water becomes lukewarm. Strange. I guessed that my check valve may no longer be working properly. However, with the pump turned off but the return line still open, the hot water stays hot in the shower (and takes a while to heat up, as expected). Given this, it feels like the check valve must be working properly.

I for the life of me can't figure out why the water would become lukewarm with the pump on but stay hot with the pump off when the return line is open in both cases. Any ideas would be greatly appreciated.

Note: I believe I've ruled out cold water crossing over into the hot water pipes by shutting off the water supply to the tank and turning on the hot water. No water reaches the faucet.

Larry Weingarten

Hi @LittleChewie , Is the lukewarm problem at all the taps?

Yours, Larry

[Deleted User]

I believe so. It's definitely in both showers. We don't run the faucets as long continuously so I'm less sure of those.

Larry Weingarten

Hi @LittleChewie , Is there a chance you could post some photos of the recirc pump and surrounding piping? This may sound strange, but I've seen recirc pumps pumping the wrong way. I've also seen hot and cold lines to the tank reversed. They seem to work fine until a volume of water is drawn and then things cool down. This is one of those cases where you don't want to assume anything! We know it will be a simple fix once the problem/s is/are discovered.

Also, by new house, do you mean just built or new to you? If just built, the builder should be helping to resolve this.

Yours, Larry

[Deleted User]

Thanks, all, for your help. I added three photos of the water lines coming into the tank, the return line coming into the tank, and the pump. The pump and surrounding piping is under a sink and a little hard to access, unfortunately.

As for the house, I mean it's new to me not a brand new house. And the hot water issue with the pump on has been the case since we moved in, but we thought it was because the tank was ~12 years old. We just replaced it (it needed replacing anyway) and the issue is still there, so I started to suspect the pump and unplugged it.

PC7060

The hot water return line has a closed shut off valve, did you close that recently when you started having problems with pump?

Also, please confirm those are stainless steel parts use for the gas dirt leg connection and not galvanized steel. 

Larry Weingarten

Hi @LittleChewie , A little story. Once I was the sixth plumber on a job to try and figure out why they were getting only a little hot water. One line on top of the tank was insulated, not the other. I ran water and the insulated line got cold and the uninsulated one got hot. This clearly showed the lines were reversed. The fix took minutes. So, run some hot water and see if the cold is actually coming in on the cold side! Then keep running hot water and feel the recirc line to see if it has cooled down. We'll help you figure this out

Yours, Larry

[Deleted User]

Hi all, thanks for the replies.

- The input line with the shut off valve is cool and the one with no shut off is warm, so I do think those are hooked up correctly? I don't have enough experience to say that with confidence, though.

- I'm not sure exactly what the check valve would look like and the pipes run behind the heater with insulation so its hard for me to access them to check for a check valve. That said, with the return line open but the pump off, the water stays warm. If there was no check valve or it were worn out, shutting off the pump but leaving the line open wouldn't solve the problem, right?

- @PC7060 yes, I shut the valve on the return line recently after I'd unplugged the pump.

- I am not sure if the parts are stainless or galvanized steel since they were there before I moved in and I'm not sure how to tell the difference.

[Deleted User]

I just ran the hot water for a few minutes and the output line with no shut off valve was very hot and the input line with the shut off valve was cold. That means they are likely hooked up correctly, right?

The fact that everything works totally fine with all of the lines open and then I get the lukewarm water just by plugging in the pump and changing nothing else makes me wonder if I am, in fact, pumping water quickly enough that I am pumping cold water out of the tank before it has a chance to heat up?

I have almost no plumbing experience before moving into this house but have I always try to learn and do what I can myself and have been trying to do extensive research and I've picked up the basics. Still, apologies if I make naive assumptions or say anything stupid. I appreciate all of the help!

BillyO

do they alway ground to the gas pipe by you? off topic but just curious

neilc

recirc pumping away ?

can you tell which way that pump is pumping?
it should be back to the tank,
post a picture looking straight down on that pump,
or look for its directional arrow

[Deleted User]

I think that might be it! Hard to get a good photo without removing the sink that the pump is under, but I think these are good enough. It does look like there is an arrow on top of the pump pointing away from the water heater. Does it look the same to y'all?

neilc

whoop, there it is , , ,

also,
isn't that a heating circ?
and should be swapped for a domestic circ ,

[Deleted User]

I'm not sure I understand the difference. This is the pump. It says suitable for "Plumbing: Hot Water Recirculation" and "Residential hot water recirculation." What is making it not suitable in this case?

https://product-selection.grundfos.com/us/products/up-ups-series-100-north-america/up-15-b-n-north-america/up-15-29-su-59896775?tab=variant-specifications&pumpsystemid=1218369944

On Home Depot, "Pump ideal for domestic hot water recirculation"

https://www.homedepot.com/p/Grundfos-UP15-29SU-1-12-HP-115-Volt-Circulator-Pump-59896775/302859597#product-overview

Thank so much for all of your help!

PC7060

@LittleChewie - “ - I am not sure if the parts are stainless or galvanized steel since they were there before I moved in and I'm not sure how to tell the difference”

To test for galvanized pipe; use a magnet to see if it sticks strongly.    Looks like stainless to me and may be fine in your area.  

PC7060

I looked at the photos from the Home Depot site and it appears the arrow in your picture and the Home Depot picture show water flowing from left to right.  This seems like opposites as @neilc said earlier 

And that looks like a nice pump for the application.  Domestic water doesn’t care other than need to be stainless which that unit is. 

neilc

LittleChewie said:

On Home Depot, "Pump ideal for domestic hot water recirculation"

I couldn't make out the model from the pictures,
this is a good application,
but needs its direction to be flipped.

PC7060

What controls the duty cycle?   That pump would only need to run 10-20 seconds to bring hot water to point of use. 

[Deleted User]

I think nothing at the moment, pretty sure they had it running continuously. Doesn't look like they had a thermometer on it since there is no other wire coming into it besides power, and there is no timer on the pump itself. I'm going to get a timer for it I think, since setting up a thermometer is probably above my skill level.

I tried flipping it today, but when I opened the shut off valve, an old pipe in another part of the line sprung a leak, so I have to get that fixed tomorrow to say for sure if it worked. But I'm pretty optimistic, definitely seems like that was the issue. Thanks again all for taking the time to help!

dhavalpatel37

Can you please let me know if you were able to solve ghe problem?

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1800152#Comment_1800152

A little late to ask this question of @LittleChewie. The last time they were on this forum was March 2021. They have a total of 8 comments. All of them were relates to the problem on this discussion. Appears the pump was installed in reverse, and if @LittleChewie reversed the flow by rotating the pump 180°, then the problem is solved and they have no reason to return here to answer your Query

To get help on your problem, you may want to post a new discussion with the particulars of your situation.