Hot water siphoning from cold water inlet into cold lines

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Lucky8926

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Somehow hot water is siphoning out of my water heater from the cold water inlet. I discovered this last summer after I planted grass seed and was watering it in the evening. I went to give my son a bath about 15-20 minutes after I shut the sprinklers off and noticed that there wasn't any hot water. The next evening the same thing happened so I turned the outside hose back on, went inside and felt the cold water inlet into the water heater. The cold pipes were hot!. The water coming out of the hose was not scalding hot, which tells me the water being siphoned out of the water heater is mixing with cold water before it exits the hose. The same thing happens when I was my clothes (I use cold water for everything except for whites). The only way to ensure this doesn't happen is to turn the hot water on before turning on the cold water, then the hot water doesn't siphon out of the heater via the cold line. If I start the washer and I feel the cold inlet going to the water heater is hot and I turn on the hot water at a faucet it barely trickles out of the hot faucet. It seems like there's a vacuum or something..... The TPR valve also leaks from time to time, not sure if this has anything to do with the siphoning issue or if it's just a faulty TPR valve.
To try and remedy this siphoning I installed an inline Heat trap (the kind with a ball), which didn't help. I also y installed an expansion tank thinking that may solve the issue. It didn't..... I'm at a loss as to what could be causing this. The water heater was installed in 2013.
Any help would be greatly appreciated!!!
 

Reach4

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I first thought to add a vacuum breaker (vacuum relief valve) if there was actual siphoning. I guess things are staying pressurized, so I am not sure that would apply here. You could add a spring-loaded check valve (one way valve) to the cold line to the WH. If you do that, you need a thermal expansion tank between the check valve and the WH.

There are things called "heat traps". They can be like slightly-leaky check valves. They come with many water heaters today.
 
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Sylvan

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When installing a water heater / tank less coil etc a decent plumbing will install a 27" loop on the CW supply to prevent stratification of cold water molecules entering the cold water supply

This loop is non mechanical and is fail safe

The reason many do not install these is because they either do not know the physics of HW stratification (heat goes to the absence of heat) or they are to cheap to use 4 Extra 90 deg fittings and do not want to "waste" the extra tubing
 

Lucky8926

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I first thought to add a vacuum breaker (vacuum relief valve) if there was actual siphoning. I guess things are staying pressurized, so I am not sure that would apply here. You could add a spring-loaded check valve (one way valve) to the cold line to the WH. If you do that, you need a thermal expansion tank between the check valve and the WH.

There are things called "heat traps". They can be like slightly-leaky check valves. They come with many water heaters today.

Yes things are staying pressurized. I have a heat trap installed; it's right above the inlet on the water heater, unfortunately that didn't fix the issue. It was the first thing I tried. Will the spring loaded valve effect the incoming water pressure?

When installing a water heater / tank less coil etc a decent plumbing will install a 27" loop on the CW supply to prevent stratification of cold water molecules entering the cold water supply

This loop is non mechanical and is fail safe

The reason many do not install these is because they either do not know the physics of HW stratification (heat goes to the absence of heat) or they are to cheap to use 4 Extra 90 deg fittings and do not want to "waste" the extra tubing

The hot water travels the full length of plumbing all the way to the fixture when cold water is turned on, so it's being pulled or siphoned out of the tank, so i'm not sure the 27" loop inline will help.
 

Reach4

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Yes things are staying pressurized. I have a heat trap installed; it's right above the inlet on the water heater, unfortunately that didn't fix the issue. It was the first thing I tried. Will the spring loaded valve effect the incoming water pressure?
Yes. Maybe 2 or 3 psi @10 gpm for a 3/4 inch model. Varies. They publish graphs. These 2 are on the lower side:
https://www.rcworst.com/Shared/content/mfr/flomatic/docs/80eto100e_headlosschart.pdf
https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Watts-0555176-Product-Overview.pdf

This is a good brand that has a little stronger spring:
http://www.simmonsmfg.com/index.php/specifications/flow-charts/
 
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Phog

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Hi Lucky, if there is crossover path between hot and cold inside one of your other house fixtures or plumbing components, this could cause the problem you're describing.

When you turn on the hose, water will flow through from the house service main to the hose bib. In a properly functioning system there should only be one single path for water to flow. But if some plumbing component fails internally and "connects" the hot and cold at a new point, you now have a second pathway for water to travel. This is a somewhat common failure for single handle showers, among other places.

In this case water will now flow through BOTH paths simultaneously (the "normal" path, and also backwards through the hot plumbing in the branch with the broken fixture). Mixed hot& cold water will flow out through the hose.
 
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Reach4

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Hi Lucky, if there is crossover path between hot and cold inside one of your other house fixtures or plumbing components, this could cause the problem you're describing.
Lucky8926 , phog brings up a good point. Go feel the cold lines under sinks or behind the tub that you can access. See if one of the cold lines is running hot..
 

Jadnashua

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If you never use hot water at your washing machine, if you have separate valves, shut the hot water one off.

Some single handle faucets, when the internals wear out, don't leak out the spout, but can allow water to cross-over between the two supplies, especially if the handle is centered between hot and cold. To check it, shut the hot line off at the wall, then see what happens elsewhere.

Water will take the path of least resistance, so that may be a mix of both lines.

If you have a hot water recirculation system, the check valve may be shot.

Heat traps aren't perfect, and it's not unusual for some heat to escape into the cold supply pipe, but that isn't enough to cause things to get really warm very far from the WH, or to last.
 

WorthFlorida

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  • Turn off all hot water valves at every single fixture in the home and run the water at the hose and check the temperature. Then open each valve one at a time and check the water temperature again.
  • If you have one of the new touch-less kitchen faucets where you leave the faucet lever open, look at that first.
  • If you use a shower head with a shutoff that is connected via a hose and you leave the faucet on and only turn off the water with the shower head, it also can cause this problem.
  • The water valve in a washing machine might cause the problem.
You can add a check valve on the cold water pipe to the water heater to eliminate the problem. However, usually the problem is noticed when you run the hot water, the cold water mixes with it and the water is never hot enough. This problem may be noticed at every sink when the cold water is turned on but never hot enough to realize the problem.
 

Phog

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In addition to agreeing with what jadnashua & WorthFlorida say above, I would like to vote against installing a check valve on the water heater. This is because, 1. It will add a new pressure drop to your house hot water. 2. It is another component that will eventually wear out & need replacement. 3. You should be able to completely fix this problem by simply finding and eliminating the crossover.
 

Master Plumber Mark

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When installing a water heater / tank less coil etc a decent plumbing will install a 27" loop on the CW supply to prevent stratification of cold water molecules entering the cold water supply

This loop is non mechanical and is fail safe

The reason many do not install these is because they either do not know the physics of HW stratification (heat goes to the absence of heat) or they are to cheap to use 4 Extra 90 deg fittings and do not want to "waste" the extra tubing



Or Why not just install a 24 inch SS flex connector and make a loop with it???
 

WorthFlorida

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According to the description, the problem seems to only occur when the cold water at the spigot is used. To me the the hose is drawing at lot of water that the water pressure on the cold side becomes lower than the hot water side, therefore water flows in reverse from the water heater because at one fixture the cold water is flowing to the hot side. I agree that a check valve may increase the water heater pressure but at the same time install an expansion tank should be installed.

Lucky, are you sure that the heat traps at the water heater were installed in the correct direction? The hot water side might be in backwards.
 
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Lucky8926

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Hi Lucky, if there is crossover path between hot and cold inside one of your other house fixtures or plumbing components, this could cause the problem you're describing.

When you turn on the hose, water will flow through from the house service main to the hose bib. In a properly functioning system there should only be one single path for water to flow. But if some plumbing component fails internally and "connects" the hot and cold at a new point, you now have a second pathway for water to travel. This is a somewhat common failure for single handle showers, among other places.

In this case water will now flow through BOTH paths simultaneously (the "normal" path, and also backwards through the hot plumbing in the branch with the broken fixture). Mixed hot& cold water will flow out through the hose.

I think this may be the issue. It looks like at one time there was an old "cowboy shower" in the basement where the washer and dryer are now. They capped the spout where the shower head was and below that there was a connecting pipe between the hot/cold lines. There are gate valves there to shut the water off, but they're REALLY old and corroded. I tried to turn them, but they're locked up. I didn't want to put too much effort into it and break them. I assume that even if the gate valves are in the closed position over the years they've failed and are allowing flow in between and pulling hot water into the line. This is right by the washing machine, which is where it seems to be the biggest issue besides the outside water spigot.

I've got my work ahead of me because these lines are super old and flush with the wall so it's going to be super difficult to get the valves off the pipes. I think i'm going to be better off just following them up the wall and into the ceiling, cutting and integraging in some pex and running them back to the washer.

Thanks for all the help everyone!! I'll keep you updated on if this was the issue.
 

Phog

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I've got my work ahead of me because these lines are super old and flush with the wall so it's going to be super difficult to get the valves off the pipes. I think i'm going to be better off just following them up the wall and into the ceiling, cutting and integraging in some pex and running them back to the washer.

Before you go ahead and do that, I would suggest doing a quick test. Get a helper to turn on the hose full blast while you feel the pipes near those suspect gate valves. If that section of plumbing is indeed the culprit you will definitely feel both the cold and hot pipes heat up from the hot water flowing backwards through that branch. If you don't feel any heat then you would need to look elsewhere.

It's also possible that you have more than one crossover point (unlikely, but weirder things happen every day). So you would want to repeat this same test for any plumbing branch that has a possible crossover.

WorthFlorida and jadnashua did a good job summarizing some possible crossover points above. In addition it could also be a faulty tempering valve, if any are installed.

Definitely do the homework and figure out exactly what needs fixing vs. what doesn't... It shouldn't take very long and may save you a bunch of aggravation. I've definitely wasted my share of time "fixing" things that ended up not being broken in the first place... haha :cool:
 

Lucky8926

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Before you go ahead and do that, I would suggest doing a quick test. Get a helper to turn on the hose full blast while you feel the pipes near those suspect gate valves. If that section of plumbing is indeed the culprit you will definitely feel both the cold and hot pipes heat up from the hot water flowing backwards through that branch. If you don't feel any heat then you would need to look elsewhere.

It's also possible that you have more than one crossover point (unlikely, but weirder things happen every day). So you would want to repeat this same test for any plumbing branch that has a possible crossover.

WorthFlorida and jadnashua did a good job summarizing some possible crossover points above. In addition it could also be a faulty tempering valve, if any are installed.

Definitely do the homework and figure out exactly what needs fixing vs. what doesn't... It shouldn't take very long and may save you a bunch of aggravation. I've definitely wasted my share of time "fixing" things that ended up not being broken in the first place... haha :cool:

Makes sense, i'm glad you mentioned this because I definitely would've been frustrated if I went through the trouble of replacing all of that and it wasn't the issue. I've already done that twice by installing a heat trap and then the expansion tank (even though the expansion tank was needed anyway).
 

Lucky8926

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What????

why not just install a back check valve on the cold inlet line going into the water heater?

I would rather get rid of the cross connection. The check valve is adding another component that may fail in the future. Getting rid of the connection fixes the issue for good.
 

Sylvan

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It is not good practice to install a check valve on a water heater because if the water heater should fire uncontrollably or incoming CW water pressure exceeds normal pressure it can cause the T&P to discharge and this is the only safety on the water heater

If there is no check valve the water can flow into the CW and HW lines which will help dissipate the pressure
 
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