Hot Water Backfeeding - Issue with Recirculating Pump and Mixing Valve

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ggrod

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Hi,

I recently purchased a house that has a recirculating pump (Taco 007-F5) with a dedicated line from the farthest fixture (master bathroom tub) back to the HWH where it ties into a mixing valve that is outside the HWH (Honeywell AMX300). When I initially bought the house I was having constant problems where the hot water was backfeeding into the cold water lines where it would come out of the cold side of fixtures. I thought I had a solution when I added a check valve to the cold water inlet, right before the expansion tank. However, I am still getting hot water backfeeding across the flexible supply line that is part of the AMX300 mixing valve and bypassing the check valve (swing check valve btw) and making its way all the way to fixtures on the top floor of the house. I can feel the hot water in the copper pipes as it bypasses the check valve and makes its way (mostly) to the branch line that services the top floor of the house (where all of the bathrooms are).

I haven't been able to determine when or why the backfeeding occurs as it does not happen all of the time but rather randomly as far as I can tell. I have at this point turned off the recirculating pump. Everything operates normally with the pump off but it does take almost 5 minutes for hot water to reach the top floor bathrooms without the circulating pump so the pump would be useful if operating correctly.

Click the following link to see pictures of my setup. At this point, I am thinking that I need to install a more robust backflow preventing device normally seen in more commercial applications in the place of the simple swing check valve I now have installed.

http://imgur.com/a/AgRH5

Any advice would be greatly appreciated.

Thanks!
 

Zl700

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A few errors in the install prior to you moving in-
The pump is a cast iron unit, should not be used in a domestic hot water application.
The pump is mounted incorrectly, never motor up.
These issues don't cause your issue but will become another soon.

Your circulator installed is too robust for your system causing bleedover by the excessive pressure on the outlet side (as little as 2-3 PSI), small but enough to cause the problem.

I suggest a proper sized domestic ciculator be installed correctly (motor horizontal), like a Taco 005 Bronze which will fit back in the same place. And get rid of the galvanized nipples, they will cause issues in the future also.
 

ggrod

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Thank you for the advice.
Looking at the specifications on the Taco 007-F5, it says that it can be used in domestic water systems. What is the reason that you think it should not be?
You are correct; the pump seems to be mounted upside down.

I was told by the mixing valve manufacturer that a solution would be to add an aquastat or temperature sensor to the circulating pump that will shut it off when it reaches temperature. Something like this:

http://www.supplyhouse.com/Honeywel...F-20-ft-capillary-Copper-bulb-sensing-element

Do you agree with that assessment or do you think my issue stems entirely from a too robust pump?

Thanks you.
 

Smooky

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Thank you for the advice.
Looking at the specifications on the Taco 007-F5, it says that it can be used in domestic water systems. What is the reason that you think it should not be?
You are correct; the pump seems to be mounted upside down.

I was told by the mixing valve manufacturer that a solution would be to add an aquastat or temperature sensor to the circulating pump that will shut it off when it reaches temperature. Something like this:

http://www.supplyhouse.com/Honeywel...F-20-ft-capillary-Copper-bulb-sensing-element

Do you agree with that assessment or do you think my issue stems entirely from a too robust pump?

Thanks you.

Something like this might be a better choice:
http://www.supplyhouse.com/Grundfos...ing-85F-105F?gclid=CLLv3vfE4s0CFUI6gQod3QgEmg

http://www.supplyhouse.com/Grundfos...ing-85F-105F?gclid=CJng7bjF4s0CFdM2gQoduFMLmA
 

Jadnashua

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The spec sheet does say the Taco 007-F5 can be used in domestic water systems for recirculation, but it is also available in either CI or SS...potable water needs to be either the SS or a different one in bronze. CI works fine in closed systems like hydronic heating because shortly after startup, all of the oxygen is pulled out by rusting things...can't do that with fresh water as it will always be supplying fresh oxygen. You might try adding a valve in line on the recirculation pipe to slow the flow a bit. Depending on the orientation and location of the check valve, it may not be closing.
 

Smooky

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It looks like the return line goes back to the hot water line. I would have returned it to the drain I think in your case. If that is not the case a good picture of that area might help.
Also what temperature is the water in the hot water heater?
 

ggrod

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Ok, thank you for the explanation. I will look into replacing the pump with either a bronze or SS version. What type of valve would I use to slow the flow? Would it be something like this:

http://www.supplyhouse.com/Watts-00...hreaded-F-Union-Inlet-x-NPT-Threaded-F-Outlet

I supposed I would install this between the pump and the HWH?

Smooky: The AMX300 mixing valve was installed with the hopes that it would make the system run more efficiently by allowing me to keep the water in the HWH at a higher temperature and mixing the water when it leaves the HWH thus also allowing for a greater total volume of how water. That is the theory as I understand it at any rate. So yes, the return line goes into the AMX300 mixing valve which is on the hot water side of the HWH. I am also more familiar with a return installation directly to the drain. I would likely have no problems if it were installed in that way.

The water in the HWH is somewhere around 130 degrees.
 

Jadnashua

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I think part of the problem lies in the mixing valve. I may be all wet, but try this for thoughts - the bimetallic valve in the mixing valve is trying to mix in some cold water to temper the hot in the tank. You're pumping water back into that valve - no cold water is flowing in, but the valve wants to add some, so the cold water inlet is open and some water can get back into the cold supply when you open any cold valve.

Running the return to the bottom of the tank might be part of the solution but may not be the whole solution. I'd start there, though.
 

Smooky

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I don't think he meant a pressure reducing valve. ....
As the instructions say, for the mixing valve, if you connect the return to the drain, only hot water will circulate when no water is running. With the heater set at 130, it is not crazy hot but you will get a blast of up to 130 F. That valve is designed to operate as it is set up. I do not have experance with that type of valve so I'm not sure what is best.

Depending on what the hot water is used for such as a heat source for the house, what type of fixtures you are filling up and how many people are in the house you may or may not need a mixing valve. If your system is large enough and not being used to heat the house, you may be able to do away with the mixing valve. The recirulating system will work better with out the mixing valve, you will get more consistant hot water.

As Zl700 said your crossflow of cold into the hot water could be happening at some other fixture in the house. Single handle showers can cause this problem. Extra shut off valves on showers and sinks or hot and cold hose bibbs that are combined can cause problems.
 

ggrod

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I was hoping to find a solution that would allow me to keep the mixing valve as part of the equation. It seems to me that this should be possible. Perhaps as ZL700 said my issue is simply too robust of a pump (as well as the orientation of the motor and the CI construction).

As I mentioned in the original post, the crossflow of cold into hot is not an issue when I turn off the recirculating pump. I have had the recirculating pump off for the last week or so to test this condition. The crossflow is 100% occurring at the HWH, where the mixing valve crosses across the top of the HWH.

Thanks everyone for the advice. I'm still a little confused as the suggestions here and elsewhere have varied greatly. I will consider everything and report back in with the results. Thanks again.
 
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