A few years ago I had a Recirculating System retro-fitted to provide quicker hot water at my sink which is a long run from the water heater. There was no way to add a dedicated return line so I have the temp-sensing interconnect valve under my sink connecting the Hot and Cold lines with Grundfos pump at my water heater on the WH discharge side.

The installation included a timer clock that I had set for 5p-9p. I soon began experiencing the problem of warm/hot ware from the Cold tap when the Recirc pump was running. Recognizing that this was a normal byproduct of this type of Recirc system, I chose to replace the timer with an On/Off switch that responds to voice control, thus the only time the Recirc pump ran was when I specifically called for it by voice allowing me to turn it off by voice when I didn’t need the instant hot water. That arrangement worked fine for about a year.

Now I am experiencing some odd behavior. I still get immediate hot water when i voice-call for it, But If I use the Hot tap at that sink when I have NOT activated the pump, I will get warm water only, no matter how long I run the tap AND I get slugs of quite cold water intermittently in the middle of the warm water flow.(Previously, I could run the Hot tap for about 2min to get fully hot water - with the Recirc Pump off - but now it never seems to run hot unless I activate the Recirc.) I also am noticing smaller spurts of cool water in the shower at night even though the shower is a good deal closer to the hot water heater and has a separate hot water line that is not common to the sink described above.

Does this sound like a symptom of a problem with the temp-sensing crossover valve? Or is there some other issue in my hot water delivery lines causing this?

there's a check valve in that system somewhere. it is faulty.

possibly it is built into the pump ?

Try just shutting off cold side angle stop to cross over manifold and see what happens.


Or remove manifold altogether.

Would that suggest that the temp sensor for the crossover has failed ?

As I understand the design, the crossover is supposed to stay open, allowing the pressurized ‘warm’ water in the hot line to flow into the cold line until it senses a high enough temperature (120d ??)then close.

Have I got that correct? So what does a failure of the temp sensor look like- does it close the valve too soon ? - or not at all ?

if the temperature sensor is at the crossover, what shuts the pump when the crossover sensor heats up ?

I don’t think the pump shuts off. I think that when the temp reaches the cutoff point ( I believe that’s 96°,) the valve closes and hot water no longer goes into the cold line.

If there is a check valve in the system, I don’t know where it would be.

Here is a link to the install brochure:
[www.watts.com]

Below is the photo of the crossover.

[drive.google.com]



Edited 3 times.

see page 4, step 2.1 of the watts manual

you may have a faulty 'manifold'

depending on age - warranty issue

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

re: SENSOR TEST. The Watts System instructions say to Turn Off the Cold Water valve under the sink where the crossover manifold is installed, Run the cold water faucet until hot water reaches the outflow, at which time the flow should slow and then stop.

In my case, the system 'sort-of' failed the test. With the Cold valve off I ran the Cold side of the faucet for about 2 minutes getting lukewarm water at normal pressure for about 2 minutes. It then began to get warmer and the flow slowed to ~ 8 oz/min. After a few minutes that flow reduced to about half (4oz/min) but never completely stopped. At this flow the water was pretty warm, probably 95°-100°.

Should the manifold have COMPLETELY stopped the flow of hot water into the cold side? And since it did not, I am guessing that the crossover manifold needs to be replaced, although it isn't clear to me why that would cause the intermittent cold water slugs from the hot water valve (my original concern.)

yes, it should STOP


manifold needs replacement

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638