Hot water coming through cold water line

Hi, I recently had a water heater installed and am having a funny issue. We are periodically getting warm water coming through the faucets when only the cold water is turned on. I've read about cross connections, but I've determined that's not the case. In fact, I've determined that hot water is coming out of the water heater the wrong way, up the cold pipe, thus warming up the water. The expansion tank was installed on the hot side, so my guess is somehow this is providing sufficient pressure and volume of water to push it out the other side.
when this happens, if I leave the water on long enough then it will get cold again, but it takes a while and I don't want to waste all that water. I think he put the expansion tank on the hot side simply for ease of installation. He suggested not even putting it in, I think because he didn't have exactly what he needed. I think he would have had to move the shutoff valve on the cold side and my guess is he didn't want to do that either. He was saying something about not knowing it was 1/2" pipe, so I don't think he had alot of 1/2" stuff. It was replaced under a home warranty, and now I'm having a hard time reaching him so I thought I'd ask here to see what the best solution is. I have no plumbing skill when it comes to soldering copper pipe, so I'll have to hire someone if something needs to be done. Might the expansion tank pressure not be adjusted correctly? If so, that's something I could do. If not, what do you suggest? A check-valve? Moving the expansion tank to the cold side? Any thoughts and suggestions would be greatly appreciated. Also, I know you can't speak for going rates in Salt Lake, but any guesses as to what would be a reasonable cost to have a plumber come and apply whatever you suggest? Thanks in advance.

Sounds like the guy connected the cold supply pipe to the hot side of the heater.

Some pictures of the piping at the hot water heater and pictures of any other plumbing work that was done when this problem occurred, might be helpful.

The pipes were installed on the right side, that's not the issue. Here are some pics - they were a little hard to get anything real clear because it's a fairly tight space, but the expansion tank is on the left on the hot side. No other work was done other than the water heater replacement. Thanks!

Ok first is there any thing supporting that expansion tank? If not then thats a disaster waiting to happen. It should be on the cold side however it will function fine on the hot, it just lessens the life of it.The short piece of pex violates code, it can not be withen 18" of the WH. Normally a PRV is on the water supply to the entire house not just to the hot water. Did he take a pressure gage and find out the pressure after the prv and then pump up the pressure to the expansion tank?

IF the small pipe sizes causes a drop in pressure when you open a cold faucet, then the expansion tank COULD push hot water out of the tank when it equalizes its pressure. Have someone open a cold water faucet while you feel the cold feed to the water heater to see if it gets hot. The easy fix is to move it to the cold side. The proper fix would be to install the proper sized water lines. your picture does NOT show us whether he has any support on the tank to prevent it from breaking the water line connection. I have no idea why anyone would have installed a pressure reducing valve on just the hot water line, but it should act as a check valve to prevent backflow.

Hey thanks for the replies. Yes the expansion tank is supported with a strap that runs around it, and is then screwed into some ducting. You can sort of see the strap in the last picture, though it's hard to know how much support it's actually providing. Yes the cold water side gets hot when the cold water only is running and gets hot several feet beyond the PRV, which would indicate I assume that the PRV is not preventing the backflow, maybe because of it's age? The guy who did the Water Heater didn't add that Pressure relief valve; I have no idea why it was put there. In fact, this house has 3 PR valves that I know of in different places. We've only lived here about 5 months so I can't say why things were done that way.

The pipe that goes to the expansion tank is larger than the 1/2" pipe (maybe 5/8" or 3/4"?). So would that cause a difference in the pressure you mentioned?

Finally, I don't know if he took a pressure reading or not. I don't have that tool or I'd check it. Should the water pressure and expansion tank pressure match?

Any ideas on cost to move it to the cold side?

Thanks again for your help!

Since its only temporary hot water, the hot pipes may be run close to the cold pipes, hidden in walls, thus heating several feet of 'cold' water.

Since he has a pressure reducing valve close up the cold inlet, one would assume the quart of water in the tank would never head up that way. I would'nt move it. Convection heating of the cold water flow up the pipe and past the PRV is a possibility.

When you have radiant heat, you get used to warm water on the cold side for the first few moments or more. So wash your hands on the cold side until it gets cold, then drink your water.

Try this. After the system has been setting a while without any activity,first turn on a hot water faucet and let the water run until it gets hot. Once it gets hot,turn it off and go to a different faucet and only turn on the cold water to see if your still getting hot water out of it.

There are two small pipes tied into the hot and cold water lines. Where does each of these lines go? You could get a cross-flow of hot into the cold at the small water line between the top of the heater and the pressure reducing valve. To prevent that from happening you need a spring check between the “T” to the small line and the top of the hot water heater on the cold side.
You need to do some detective work to determine what is happening. Go turn on the hot water somewhere in the house. Put your hands on the pipes at the top of the hot water heater. You should feel one line getting cold and the other getting hot. Then shut off the hot water and turn on the cold faucet that you notice has warm water. Put your hands on the each of the water lines to determine if hot water is going up into what is suppose to be the cold line.

I appreciate all the responses. Once again, I've already determined what is happening - that is that hot water is coming through the wrong way through the cold pipe when just cold water is turned on. I've done a number of things to determine this, some of what you are suggesting. The big tell-tell sign to me is that before turning on any water I can feel the cold side pipe and it might be warm a few inches from the connection to the water heater due to convection. If I turn on the cold water at a faucet, the heat then "travels" up the cold water pipe several more feet. Also, when I turn off the water, I can still hear the sound of running water going back in the water heater, at which point the cold side pipes feel very cold.

The small pipes go to the humidifier for the furnace on the hot side (this doesn't get used), and I think the one on the cold side was for an old swamp cooler that's no longer used.

Hackney plumbing: I'll try what you suggest and report back.

ballvalve: It takes too long to cool down to simply live with it. I do like the suggestion of washing the hands with just the cold side though.

The potable water expansion tanks' instructions say to only install them on the cold side. There are at least two reasons for that. One, the bladder is not designed for hot water and it will fail prematurely, and two, it could be holding at least a quart or more of potentially hot water (even if it's cooled off, if it discharges water back into the tank, what's there is hot). Depending on how far the fixture is from the WH, the pipe routing, and the relative pressure and restrictions, when you open a cold line, the pressure in the expansion tank might push hot water out into the cold supply. The lower the fill pressure in the tank, the more water it will hold at any water pressure level, so it could be more than that. you can only check and reset the expansion water pressure when there's no water pressing on the inlet - i.e., the water is turned off and a faucet is opened to relieve the pressure; otherwise, it will just show the water pressure, not the air pressure.

A couple of screws into a duct may or may not hold the tank when it fails (say it's a 4gallon tank, that's 32 pounds of water plus the metal)...that might be enough to ruin your day if it causes something to leak when it falls.

The Pressure reducing valve should stop any back flow, so you must have a poltergeist.

When you open a hot tap, the cold water cannot flow in the opposite direction. I dont care where your bag in a can is located.

I love replies such as this post has generated, they are well interesting.
It appears ( to me ) that the h/w and c/w lines are in 1/2"? Perhaps the whole illustrated area should be cut out and rejigged, and re-piped? What size is your water service?
Perhaps the unused lines to the humidifier and the cooler should be abandoned and capped off. At the moment, both have warm water sitting in them.
Could the OP post a full length pic of the w/h; given the oddities above there might be more down below. I notice that a seismic strap is loose.
What views do others have on the 3# PRV's in the house?

I love replies such as this post has generated, they are well interesting.
It appears ( to me ) that the h/w and c/w lines are in 1/2"? Perhaps the whole illustrated area should be cut out and rejigged, and re-piped? What size is your water service?
Perhaps the unused lines to the humidifier and the cooler should be abandoned and capped off. At the moment, both have warm water sitting in them.
Could the OP post a full length pic of the w/h; given the oddities above there might be more down below. I notice that a seismic strap is loose.
What views do others have on the 3# PRV's in the house?

I think your hot water is just working its way up the pipes when at rest - see the links.

http://www.siouxchief.com/Supply/Fitting-and-Valves/Sweat/Heat-Trap-Loop.M7LUX

http://www.waterheaterrescue.com/pa...g/Tanklets/water-heater-heat-trap-issues.html

http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13100

Well, I finally got this all resolved so I thought I'd come back and report. First off for Hackney plumbing: I never did try exactly what you had mentioned so I can't say what the result of that was. To ballvalve: regarding your comment: "When you open a hot tap, the cold water cannot flow in the opposite direction. I dont care where your bag in a can is located." You're right, and this was my "fix" for getting cold water more quickly - turn on a hot water tap at another location, then turn on the cold where I was getting a drink. Since the hot water can't flow both ways that seemed to do the trick.

But more to the point, this morning the original plumber finally came back and took off the expansion tank from the hot side and put a new smaller one on the cold side. This seems to have fixed it as was expected. Yea!! He said he had never seen that happen, but was nice enough about it. I just wish he wouldn't have been so hard to track down and get out to fix it. But, all's well that ends well I suppose.

All of the installation instructions for an expansion tank call for it to be on the cold side...the ones designed for potable water are NOT designed for use on hot, plus, some of the other issues you noted. On the cold side, any that might discharge would be cold, not creating any problems, and being cold, the bladder should last a much longer time as it was designed for.

They do make expansion tanks for boilers that go on the hot side (obviously!), but they are specifically NOT designed for potable water.

But, when setup properly, you rarely should get much more than a cup or so of water pushed into the expansion tank during a reheat situation. It sounds like the static pressure in the tank was low for your local water pressure, allowing much more hot water into the tank, making the problem worse, and stressing the expansion tank as well.