Hot water backflowing

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Dan87

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Hello all!

Long time reader, first time poster. I recently re-plumbed my entire house, supply lines, drain system, all new faucets and fixtures...the works. This was relatively easy since all of my plumbing is right on top of each other straight up through the house, although still a lot of work never the less. Everything works perfectly except for one detail. The hot water back tracks into the cold supplies, not when in use, but when dormant. I live alone, so not much water gets used, but when the lines get flushed for a few seconds (3-5 seconds) temps are normal. When I get home from work (water hasn't been used in about 10 hours), the cold supply going to the water heater is hot all the way back to the PEX manifold. Now, I originally thought this was possibly due to the water heater being so close to the manifold, but my oil burner supply is doing the same thing, and that is located on the other side of the basement, about 25 feet of piping away. The only reason I can surmise is because I have two independent water heating systems feeding the same manifold? The reason for this is the fact that my oil burner type is a "summer-winter" hook-up, and needs water flowing through it all the time, and needs to maintain a warm core temp all of the time (or so I've been told and research has told me).

So, the PEX manifold utilizes the bottom 3/4" inlet for the main feed, then the top 3/4" ports are used for the water heater in and out. The oil burner is fed and brought back through the standard 1/2" distribution ports. I know, this means I'm using both oil and electric to heat my hot water, but my logic is that since the water heater is using 3/4" pipe and the oil burner is using 1/2", more of my hot water will be pulled from the water heater than from the oil burner, allowing the oil burner to still run as needed. This being my first summer in the home, I think I burned about an 1/8" of a tank of oil, which works for me. While I'm on the topic, I debated on using the water heater as a "pre-heater" to the oil burner, which would theoretically mean the oil burner would fire up far less frequently. However, not knowing if that was a good idea I didn't do it that way. Further discussing the topic with other people, they noted that bringing in water at a temp only 10-20 degrees below what the aqua stat is set for, may cause the oil burner to not fire long enough to burn properly, causing excess carbon/soot build up in the unit. Any thoughts on this are welcome as well!

Anyway, back to the back tracking. Both the oil burner and water heater have thermal expansion tanks right near them (as seen in the pic of the water heater), and I checked it's pressure prior to installation and it is correct. While installed, you can hear that it is mostly air inside when you tap it (and some water at the top). The bottom line is all of my cold feeds off of my manifold get warm, and the first 2-3 seconds of cold water at a tap is warm, then gets cold. If you run the hot side of a faucet for a few seconds to a minute, and feel the cold feeds to the water heater or oil burner, they immediately get cold, as cold water is now flowing through them. So, it doesn't seem as though the water is "back flowing" as I've heard so much from people, as it is "back tracking", because it's happening when nothing is in use, and corrects itself as soon as water is flowing. The back tracking warmth actually heats up the cold side of the manifold and warms up all of the cold feeds for about 12 inches off the manifold. Any input on this would be much appreciated. Sorry for the lengthy post, but I needed to be thorough. Thanks!

PEX manifold and GE Geospring water heater
1.jpg


PEX Manifold Port Usage
2.jpg


Cold water supply to water heater that gets hot
3.jpg


Oil burner cold supply that gets hot
4.jpg
 

Smooky

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I would tye the blue pipe labeled "Boiler Cold" into the cold pipe coming out the top of the manifold. I would install a back flow preventer in the blue pipe just above the manifold. Then just past the location of the thermal expantion tank is where I would tie the boiler cold pipe in. My thought is the "Boiler Cold" water is not really cold.
 

CountryBumkin

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+1 what Smooky said.

I would do two more tests.
1) Is the copper pipe feeding into the water heater warm?
2) If you shut off the Boiler feed (cold side) does that correct the problem?
 

Dana

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BTW: How long has the GeoSpring been in service? Any feedback/comments as to it's performance?
 

Dan87

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+1 what Smooky said.

I would do two more tests.
1) Is the copper pipe feeding into the water heater warm?
2) If you shut off the Boiler feed (cold side) does that correct the problem?

1) Yes, the feed to the water heater (cold supply) is warm, often hot, from the manifold to the inlet on the water heater, often hotter than the exit pipe off of the water heater (hot side). But, remember, this is only after sitting dormant. Once some water is used, the water heater feed becomes ice cold as the water starts moving through the water heater, which is the same scenario for the oil burner cold feed.

2) I will give that a try, but something tells me that I tried that already.

As for piping the boiler feed off of the top 3/4" water heater feed, I don't see how that will change anything. The manifold is nothing more than a large multi-branch-tee of sorts. The entire cold side is pressurized with the same pressure, moving the 1/2" boiler feed off of the manifold to the 3/4" pipe coming of off the top shouldn't change anything, as in theory that 3/4" cold supply to the water heater is just an extension of the manifold when you think about it.

Thanks for the suggestions, keep them coming!
 

Smooky

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The backflow preventer will prevent any warm water from getting into your cold water. By connecting the water line labeled Boiler Cold into the inlet pipe going into the hot water heater you are able to separate it with the back-flow preventer. This way your cold water will stay cold and there will be no warm water mixing in. Also the expansion tank should last longer if it is not constantly exposed to hot water. That is why I said to connect past the expansion tank. The back-flow preventer needs to be in the cold water line after the manifold and before the expantion tank and where you tie in the "Boiler Cold" blue water pipe.
 
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Dan87

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BTW: How long has the GeoSpring been in service? Any feedback/comments as to it's performance?

I installed the GE GeoSpring water heater about 6 months ago, no complaints! I have been installing these for the company I work for since the first version; the one I have the newest version and GE's 3rd revision of the product. The first one was made in China, the 2nd, and 3rd (this one) are US built. The first two models had some kinks that they needed to work on, but this 3rd version seems to have them worked out (knock on wood). I recommend them to anyone that has a standard electric water heater and is looking to upgrade. Just make sure that the installation is done to manufacturers specifications; their are minimum air clearances required around the unit, as well as condensate drain lines that need to be ran. As old school as I am (I do prefer the simplicity of a good old Bradford White), I figured if I was going to go modern and and efficient with my remodel (PEX manifold, etc.), I shouldn't skimp on the water heater. Also, most electric utility companies have generous rebates available for installing one in your home when replacing an old unit, anywhere from $250-$400.
 

Dana

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Thanks for the feedback on the GeoSpring- that was my impression too, but don't have a lot of first or second hand comfirmation thereof.
 

Dan87

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The backflow preventer will prevent any warm water from getting into your cold water. By connecting the water line labeled Boiler Cold into the inlet pipe going into the hot water heater you are able to separate it with the back-flow preventer. This way your cold water will stay cold and there will be no warm water mixing in. Also the expansion tank should last longer if it is not constantly exposed to hot water. That is why I said to connect past the expansion tank. The back-flow preventer needs to be in the cold water line after the manifold and before the expantion tank and where you tie in the "Boiler Cold" blue water pipe.

Ok, I understand what you are saying however I still feel like a back flow preventer shouldn't be necessary. Although it may make the problem go away, I can't help but feel like it's just fixing the symptom, not the actually issue; in a properly function plumbing system, you shouldn't have hot water back flowing to the cold side. What seems really odd is that both the boiler and water heater cold feeds are back flowing, and it happens when nothing is in use.
 

Smooky

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Is there a recirculating pump on the system? If there is a recirculating pump , where is it located and which way is the flow? This is important because pressure is not even around the loop. There is positive pressure in front of the pump so hot water can be pushed into the cold. Behind the pump, on the suction side, cold can be sucked into the hot. Systems with recirculating pumps are lots of fun without properly placed back-flow preventers. On some systems you may get a natural flow since hot water rises and cold water sinks.
 

Cwhyu2

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Okay I know this is a long shot but maybe the dip tube in the water heater has become dislodged at some point during installation.
Just a thought.
The reason is and I`m sure you know this as the dip tube sends the cold water to the bottom of the tank as the water heats it will
rise to the top of the tank the dip tube also keeps the hot water from rising back into the cold feed.
Once again just a thought.
 

Dan87

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Update: So, I decided to isolate the water heater. I left for work yesterday morning and shut both the inlet shut off valve and outlet shut off valve for the water heater. I got home and touched all of the water pipes, hot and cold. None were even warm, even going back to the top of the water heater, the pipes were cool to the touch all the way to the top of the water heater. Same thing for the oil burner, the cold water feed and hot water out were cold all the way back to the boiler. So, although I am fairly certain the water heater is the problem, I'm not understanding how the water heater would cause the boiler inlet and outlet lines to back flow. So, today I am isolating the boiler by shutting both the inlet and outlet to the boiler. If that also corrects the problem, then I know the issue is being caused by having both heating systems running simultaneously.
 

Dan87

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Is there a recirculating pump on the system? If there is a recirculating pump , where is it located and which way is the flow? This is important because pressure is not even around the loop. There is positive pressure in front of the pump so hot water can be pushed into the cold. Behind the pump, on the suction side, cold can be sucked into the hot. Systems with recirculating pumps are lots of fun without properly placed back-flow preventers. On some systems you may get a natural flow since hot water rises and cold water sinks.

There are no recirculation pumps in my system.
 

boatracer

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For the "Boiler Hot" connection, is the flow on that line into the manifold from the boiler? If that is the case, when you are away from the house and the boiler is running, there is no water flow within the system. The boiler circulator pushes water into the HOT side of the manifold and the only place it can go is backwards through the water heater and to the cold side of the manifold.

When you isolated the water heater was there any adverse effects on the boiler operation? Cause then there would be no cross connections between hot and cold for the water to go.
 

Dan87

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For the "Boiler Hot" connection, is the flow on that line into the manifold from the boiler? If that is the case, when you are away from the house and the boiler is running, there is no water flow within the system. The boiler circulator pushes water into the HOT side of the manifold and the only place it can go is backwards through the water heater and to the cold side of the manifold.

When you isolated the water heater was there any adverse effects on the boiler operation? Cause then there would be no cross connections between hot and cold for the water to go.

Bingo. I took your advice and looked it at from that angle. What I noticed is that the boiler feed (cold line) is hot off of the manifold but only to a point traveling back to the boiler, which means it's creating a loop. The hot water from the boiler is pushing back to the manifold as you said, then traveling backward through the hot outlet of the water heater, back out through the cold side of the water heater, back into the manifold, and then into the cold feed to boiler. With that said, I think you are completely correct. I'm going to assume I'm experiencing this because I have two different heat sources on the same plumbing system, but regardless it still seems strange.

It would seem that one solution would be to put an back flow preventer on cold water supply of the water heater? I will say that after doing some searching, I don't really know what the correct back flow preventer would be for this application; I've never seen one. So if someone could point me in the direction to a back flow preventer for this application, that would be great. But, my other option is to just eliminate the "summer-winter hookup" on my boiler all together. My heating guy told me (back before I put the water heater in), that if I go with a water heater, he would advise capping off the DHW coil in the boiler, and just make a "cold start" boiler. I've been looking into that ever since he mentioned it me, and I continue to get mixed feedback. One person tells me that it's ok to do that, the next person says that you can ruin a boiler doing that because it needs to maintain a certain core temp all the time. My boiler is an EFM PK-750 for reference. I know this question is not new and is talked about a lot, but any thoughts on this? Also, since this thread topic has shifted gears, should I move this question to a different forum? Thanks for all of the input!!
 
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