# Hot Water Recirc Pump Check Valve Needed?



## seabeast (Jul 30, 2013)

*Good question, here's what I know...*

I'll admit up front that I don't have a definitive answer for you. But I have some info that might be helpful.

The stated purpose of this valve is to prevent "thermal cycling", in which the heat differential between the two legs of your recirculating system cause the water to circulate on its own. Basically, hot water rises, so if one side is hotter than the other, the hot water will move to the highest pipes in your house. This is how passive or thermal recirculating systems work. This is fine if the water moves in the direction you want, but counter-productive if thermal cycling causes the water to move backwards (you want the hottest water near the fixtures, and cooler water in the return lines). For example, if hot water from the HW heater flows backwards through your pump, the pump will see the hottest water and believe the water is all hot and thus won't turn on, even after the rest of the house pipes have cooled. The internal check valve makes sure that water only flows in the proper direction (from the pump towards to HW heater).

Note that many recirculating system pumps have internal check valves. My system uses a Grudfos "UP 10-16 BU/ATLC", which has an internal valve. You should check the specs for your pump.

In my case, I'm having a problem with hot water coming out of my cold water pipes for a minute or two after the cold water is turned on, and every plumber I've spoken with immediately claims the problem is due to a bad or missing check valve in the recirculating system. So I believe you'll find a lot of people who will tell you a check valve is critical.

I'm personally not so sure.

It makes no sense to me that a check valve can cause hot water to infiltrate my cold water, since I have dedicated hot water return lines so there should be no loop through the pump that includes the cold water lines. When I pressed the most recent plumber to explain how this worked, the only reason he could give was that he's a plumber and I'm not. Seriously. That was before we knew my pump had an internal check valve, anyway. This pump was installed by the previous plumber I hired to try to fix my hot/cold problem. It's a nice pump, but didn't help the problem, check valve or not.

If your new install is a retrofit in which they use the cold water lines as the hot water return, then all bets are off. They use trickier valving so I can't really comment on the value of a check valve.

I'll be following this thread to see what others have to say, since this issue is very much on my mind.


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## Ghostmaker (Mar 2, 2013)

http://www.taco-hvac.com/uploads/FileLibrary/100-41.pdf


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## Eyeneedhelp (Nov 6, 2010)

seabeast said:


> Note that many recirculating system pumps have internal check valves. My system uses a Grudfos "UP 10-16 BU/ATLC", which has an internal valve. You should check the specs for your pump.
> 
> In my case, I'm having a problem with hot water coming out of my cold water pipes for a minute or two after the cold water is turned on, and every plumber I've spoken with immediately claims the problem is due to a bad or missing check valve in the recirculating system. So I believe you'll find a lot of people who will tell you a check valve is critical.
> 
> ...


 
I have the Grundfos UP-10-16 B5/ATLC which doesn't have an internal check valve like yours does. And I will install a check valve to prevent the hot water movement in the wrong direction when the pump is off.

I too get luke warm water out the cold water faucets but only on the last two faucets before the pump. I was thinking it was my shower mixing valve bleeding hot water to the cold water pipe.

I'll set the pump to be on all the time, until I can sweat in the check, to see if that helps my luke warm water coming out the cold faucet. 

Also this is a Real Hot water circulation piping system (just completed new house construction) and not the hot to cold you describe, so we are on the same page.


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## TheEplumber (Jul 20, 2010)

markstg said:


> Hi,
> 
> I have a hot water recriculation piping installed in my residence. The hot water return pipe is brought to the water heater through a pump installed at the water heater drain. The pump is time and aquastat controlled, so I would think during the off periods it would provide backflow protection. My plumber did not install a check valve after the pump and I requested he do that, and he says it is not needed and that as the "Plumber" he knows more than me.
> 
> How important is the check valve? What can happen without one?


I have always piped a normal WH recirc through the CW supply
I have also always installed check valves on the CW inlet and the HWR.
Reason why is because the majority of my training and work has been commercial where the systems are detailed by engineers- so I did what they said.
People will argue for their method of installation until the sun sets but I have not seen any definitive answers as to which way is better.

Sent from my iPhone using DIY Forum. Watch out for spell check


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## Ghostmaker (Mar 2, 2013)

TheEplumber said:


> I have always piped a normal WH recirc through the CW supply
> I have also always installed check valves on the CW inlet and the HWR.
> Reason why is because the majority of my training and work has been commercial where the systems are detailed by engineers- so I did what they said.
> People will argue for their method of installation until the sun sets but I have not seen any definitive answers as to which way is better.
> ...



The reason you use 2 check valves is to prevent gravity flow and back flow.


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## seabeast (Jul 30, 2013)

*I may be overthinking this, but...*



markstg said:


> I have the Grundfos UP-10-16 B5/ATLC which doesn't have an internal check valve like yours does. And I will install a check valve to prevent the hot water movement in the wrong direction when the pump is off.
> 
> I too get luke warm water out the cold water faucets but only on the last two faucets before the pump. I was thinking it was my shower mixing valve bleeding hot water to the cold water pipe.
> 
> ...


A real plumber may want to pipe in here, but I'm guessing you're better off installing the check valve between the pump's output and the WH return connection. If there is non-descending piping from the WH connection up to the pump, it seems possible you could get convection flow of hot water from the WH to the pump, which would again confuse the pump's temperature sensor.

-Seabeast


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## Ghostmaker (Mar 2, 2013)

I'm a real plumber and eplumber is a real plumber. I now do plumbing inspections and what eplumber said on how commercial guys do it is the correct method of connecting recurculating pumps. 2 checks and through the cold inlet.


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## seabeast (Jul 30, 2013)

Ghostmaker said:


> I'm a real plumber and eplumber is a real plumber. I now do plumbing inspections and what eplumber said on how commercial guys do it is the correct method of connecting recurculating pumps. 2 checks and through the cold inlet.


I believe that's how you do it for new installations.

What I'd like is a compelling explanation of HOW this will fix my problem. Please don't take this the wrong way, but "I'm a real plumber" is a very unsatisfying explanation, especially to an engineer like me who previously spent $700 based on that explanation.

As I see it, the only substantial difference between what you suggest and what I have is a cold water check valve. My system used to work fine without that check valve, but now it doesn't. Is it reasonable that the missing check valve only became a problem recently? What path do you believe the hot water is taking to get into my cold water pipes?

One theory I toyed with is the possibility of the incoming water pressure to my house fluctuating. Maybe that could siphon some water out of my water heater, giving it a chance to enter the cold water pipes when pressure returns. But since my house system is closed other than the cold water input, that doesn't really make sense to me. It shouldn't be possible to drain the house without air getting sucked into faucets or taps, which we'd surely notice when we next turned on the faucets.

Is it possible for the water heater to be only partially full, and thus for there to be compressible air inside? We don't get air blasts from our hot water faucets, so I expect that to mean the WH is totally full.

-Seabeast


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## Eyeneedhelp (Nov 6, 2010)

Ghostmaker said:


> I'm a real plumber and eplumber is a real plumber. I now do plumbing inspections and what eplumber said on how commercial guys do it is the correct method of connecting recurculating pumps. 2 checks and through the cold inlet.


 
By Real Hot Water Recirculation System, I meant there is a return hot water pipe to the water heater, not the kind that uses a temperature valve to bleed hot water line to cold water line at the furthest user. 

Whether the dedicated hot water return line is connected through the pump to the CWS to the water heater or the Water Heater Drain (with check valves installed as ya'll describe) seems to be a preference as both work in a simple Residential system.

I think plumbing engineers show connecting the hot water return pipe to the CWS water heater inlet could be they don't want to interfere with the drain connection and/or they feel sending the warm return line water to CWS and then into the Water Heater sends the water thru the water heater as the manufacturer designed the water flow through the water heater. 

Anyway thanks for answering the question why the check(s) are needed, and I'll be installing one on the discharge of my hot water recirc. pump.

I do appreciate SeaBeast probem with finding the problem with his system of hot water coming out of a cold water faucet, as once all Best Practices have been implemented, the problem hasn't gone away, and changing many parts til it goes away seems to be the method plumbers use to correct this problem.

thanks


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## ahprojects (Mar 13, 2020)

There's an important step in starting up a new hot water recirculation system that has not been mentioned. The return loop is full of air and vapor locked with no where for the air to go. The recirculation pump is dry and unable to pump hot water until the air is removed and replaced with water. A temporary bleed is needed past the outlet of the pump and check valve to vent :wink2ut the air before the pump will flow water. Not recognizing this can result in overheating the pump & possible failure.


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