Troubleshooting Grundfos hot water recirculation

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Rmk9785e

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We have been using Grundfos UP15-10SU7P/TLC recirculating pump with our water heater for about 10 years. We had to replace their plastic valve with Aquamotion Flash by-pass valve and it has been working fine. Last night we were not getting hot water and I thought perhaps the water heater may have stopped working. Checked this morning and found the water heater was working fine. I unplugged the Grundfos pump and was able to get hot water at the faucets after a few minutes so I'm wondering if the pump is not working. When I plug in the pump, it hums for about 10 seconds and then goes quiet. It use to hum all the time when it was running.
I couldn't find any troublshooting manuals at Grundfos site and I'm woundering how do we troubleshoot the Grundfos pump. Is it time to replace the pump? Any advice is appreciated.
 

Rmk9785e

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you should get a grundfus with a timer on it probably gonna run about 350 bucks ....
That is exactly what we have now and I'm trying to figure out whether the pump or the under-sink valve needs to be replaced.
My question remain regarding troubleshooting the component (pump or valve) that doesn’t work.
Is 10 years the limit of useful life for the pump?
 

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Jeff H Young

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no matter how long you run it you get no hot water? when pump runs the valve under sink remains cold?
 

Rmk9785e

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no matter how long you run it you get no hot water? when pump runs the valve under sink remains cold?
If I run the faucet, warm water arrives a few minutes later. I do get hot water sooner on a faucet close to the water heater.
Currently, the valve under the sink remains cold no matter how long the pump has been running or whether the pump is running. Picture of the valve is attached. This pump/valve combination has been running well until last night.
We’re in California Central Valley where temps hover in the upper nineties so it’s not cold outside.
 

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Jeff H Young

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turn cold water anglestop off under sink open cold water on faucet water should come out a little cool at first and when warm it sould stop . that is a check for your valve under sink.
did you try turning pump on manual on? Pump might be frozen you mentioned 10 second run might shut off and cool down . with water off remove pump 4 screws pull pump might be siezed
 

Rmk9785e

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turn cold water anglestop off under sink open cold water on faucet water should come out a little cool at first and when warm it sould stop . that is a check for your valve under sink.
did you try turning pump on manual on? Pump might be frozen you mentioned 10 second run might shut off and cool down . with water off remove pump 4 screws pull pump might be siezed
Thank you. I did the following per my understanding of the instructions:
1-Turn pump on (it’s always on manual)
2- Turned off cold water supply under the sink.
3- opened the cold faucet and let it run for 10 minutes. It kept on delivering hot water. The valve was also warm.
4- Turned on the cold water supply under the sink.
Are you recommending I remove the pump and open it up? I do not have new gaskets if any of these require replacement.
 

Jeff H Young

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Sorry I thought you had a grunfos valve the "comfort system" trouble shoot could be differant . the grundfos valve would be bad if you tested in this manner

Can you tell if pump runs or not ? If you test as we said above and run pump on manual will it continue to run? or still shut right down? if it continues running Id replace the valve I meant will pump continue running
 

Rmk9785e

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The pump buzz stops after 8 seconds but it seems like it keeps running and not as loudly because if I switch it off then it goes totally quiet.
Looks like the steps above have unstuck whatever was not working. Now it works and the valve is warm indicating hot water flow.
Thank you for the handholding.
 
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Jeff H Young

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pump might have been siezed running water getting it good and hot might have broke it loose again.
 

Rmk9785e

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pump might have been siezed running water getting it good and hot might have broke it loose again.
It was premature to declare victory. This morning it was the same situation. Closing the cold water supply under the sink and opening the cold faucet brought hot water after a few minutes. I'll try replacing the Aquamotion Flash valve today and report back if that fixes it otherwise I'll contact Grundfos support on Monday to troubleshoot the pump and perhaps replace it.
8/9/22 update: Replacing the valve did not change anything. I opened the Grundfos pump and observed that the rotor was having trouble moving. Replacement Grundfos pump cartridges are selling for a little over $200 so I bought a new Watt recirculation kit for $199 at Home Depot and installed it.
Problem solved. Thank you all.
 
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Rmk9785e

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Sometimes it is better to leave things alone. Everything was working fine until this. We were traveling for a couple of days and I unplugged the Watt recirculating pump. I plugged it back when we returned home. The pump is buzzing but no hot water is circulating. The Aquamotion Flash valve remains cold. The WH is working fine and we get hot water after running (and wasting) water for 10 minutes. Is it possible the pump has seized because of this power cycling? How does one test the pump?
 

Rmk9785e

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When the pump comes on the pipe (recirc line) gets hot. That means it's working.
Is it possible that the pump and the hot water line are getting hot simply because of conduction from hot water in the tank?
If the pump is working and the humming is not caused by its seizing then where is the hot water going while the only recirculating valve is cold?
 

John Gayewski

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Is it possible that the pump and the hot water line are getting hot simply because of conduction from hot water in the tank?
If the pump is working and the humming is not caused by its seizing then where is the hot water going while the only recirculating valve is cold?
Is possible convection is heating the line, but what I said is. "When you turn the pump on". Convection won't be as fast as a pump so even if you are circulating you should be able to tell if the pump is pumping, by the temp change as you turn it on.

So you'll have to leave it off for a while, check temp, then turn on and check temp. The end of the recirc line will be hot if the pump is running, if convection only the temp will be lower.
 

Rmk9785e

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Is possible convection is heating the line, but what I said is. "When you turn the pump on". Convection won't be as fast as a pump so even if you are circulating you should be able to tell if the pump is pumping, by the temp change as you turn it on.

So you'll have to leave it off for a while, check temp, then turn on and check temp. The end of the recirc line will be hot if the pump is running, if convection only the temp will be lower.
Thank you for helping troubleshoot. It appears the pump had somehow become stuck. I contacted Watts customer service and received instructions on how to examine whether the impeller is rotating. I was able to free it up and it’s working now.
 
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