I recently began getting hot water out of the cold water taps in my house. I've read that this is caused by hot water leaking across mixing valves or washing machine valves. I turned off the washing machine valves and still have the problem. I have 3 Price Phisher single lever shower fixtures with anti scalding valves. I assume that is where the problem is. Is there a way to isolate these valves one at a time to find out which one is leaking hot water to the cold water side? Is it the mixing valve that causes this problem? The house is 7 years old and has the original water heater and hot water re-circulating pump. No plumbing work or repairs have been done recently.

Thanks for any help, John

Try closing a valve on the recirculation system and see if it stops happening.

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There are no valves on my re-circulating pump. Do you mean the shut off for the hot water line? Are you suspecting something other than what I think is the problem? Please elaborate. Thanks for the help, John

you need to shut off the recirculation system not the hot water. sometimes recirc. systems can cause your problem

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The recirculating pump creates a small differential pressure of hot vs cold. Therefore, if there is any path for water to flow from hot to cold, it will. A defective Moen cartridge, and especially any MIXET brand tub or shower, can allow this to happen. If you happen to have a shower head with an onboard shutoff button, and you leave the water turned on at the valve and shutoff at the button, it will happen.

After not using any taps for a few hours, go around and feel the valves, feel the pipes under the sinks, take the chrome plate off the tub/valves to feel those. This should help you identify the culprit.

Thanks Jimmy. I will shut off all the hot water valves that I can and see if I can find the valve that's leaking. The Price Phisher shower valves I have are the single lever kind that you just turn without pulling. I took the lever off, but the decorative chrome disk is held on by a ring that appears to be screwed down. Does that take a special tool to remove without damaging it? I tried to gently unscrew it with channel locks, but I was afraid I'd mess it up. Thank you for your help, John

Stop! Before you break something! Lets find out where this cross connection is first!

You do not want to shut off everything to do with the hot water you just want to stop the recirc for now. If you can't figure out how to do this you just may want to hire a plumber. If you go into this 1/2 cocked you may create a situation where a plumber will have to fix broken things that initially had nothing wrong with them!

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Maybe I should explain my though process on this problem. I have had this hot water recirculation system since the house was new 7 years ago, and it has always worked fine. We have not had any plumbing repairs or changes. The hot water out of the cold water taps just recently started happening. I have 5 faucet/shower valves that are single handle mixing type. I have isolated the kitchen, service sink, and wash machine by turning off the hot water valves. The problem was still there. That leaves the 3 shower mixing valves as the only source of the leak. Once I figure out how to get the decorative cover off, I'll be able to shut these off one at a time until I find which one is leaking the hot water into the cold line. Does this make sense? If you have some other process for finding the problem, please tell me step by step. Thanks, John

Take the cover plates off, get the problem to show itself at a cold water faucet and then feel the cold pipe of each shower valve until you find the one getting hot. This will find the cross-connection if the shower valves are causing it. I would also make sure my circ pump was not causing the problem.......it would be the easiest thing to check anyway.

You may not be able to turn off individual shower valves.

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Britt, In what way could the recirc system be the cause of the problem? It appears to be working as it always has. Thanks, John

The dynamics of a plumbing system almost always cause the dynamic hot water pressure to be less than the cold, so it should be the other way around. There are conditions, such as a broken hot water line under a concrete slab, that will cause your symptoms, but it requires an onsite visit to diagnose the system.

You dont need to turn off the showers. You take the cover plates off the single lever shower valves and make the problem of hot coming out the cold faucet at a lavatory........while this is happening, feel the cold side pipe of the shower valves and see if it gets hot......this way you can see if the shower valves are where its crossing over at...You dont run the showers or turn off integral stops for the showers.

You lost me on that one. I have no clue what you talkin about now. Sounds like a cross connection to me. Where you gettin a leak under the slab from that?

Stick around long enough and you will learn. The cold water usually has to go all the way to the heater and then back again which creates more pressure drop than the cold line, and if that is the case, the hot cannot gravitate into the cold system. BUT a hot water leak under the floor WILL create a hot pool which will heat up standing water in the cold line which will have to be removed and then the incoming water will flow fast enough that it will not get heated until it is shut off again. THAT is where I get it from, plus many years of seeing it happen.

He doesn't have a leak under the slab. I know exactly what your talking about the leak heating up the floor,etc. But the water would cool quickly once the cold started flowing. The way the cold water is ran doesn't matter. You have less hot pressure than cold because your using the cold to force the hot out of the tank,not to mention the volume difference through a 5/8 dip tube. A cross connection is causing his trouble somwhere, and what i posted is a way to check and see if its with his shower valves.

I might learn somthing, but thats jiberish........So your saying a cross connection cant happen because of the way the cold line runs to the water heater and then hot goes to the faucet? A cross connection happens when a cold and hot line are connected together without a backflow device. It has nothing to do with where the pipes are ran. The water temp will go all over the board......from too hot to too cold or anywhere in between. I'm glad others will read this. You will learn somthing here i promise. Of course cold will run to the water heater to supply the hot..........just like any other house. The shower cartridges can malfunction causing a cross connection. I have found many moens like this. Your too much of a smartass for your own good. I bet you make an ass of yourself all the time.



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After 55+ years in the business, most of it troubleshooting, I doubt it. I have had more than one plumber change a water heater because the customer was not getting enough, or any, hot water, even though I told him it was probably a leak under the slab. In fact one brought the new heater back because it was doing the same thing as the old one and wanted a credit for a defective water heater.



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You know so much your confusing it all upstairs.

Well that guy was an @#$%&. He jumped to a conclusion or just wanted to sell somthing. Would it have been too hard to turn off the cold supply........wait a few minutes then turn the valve back on? If he had done that he would have heard the heater filling back up, and knew it was a leak. Theres alota ways to check for a hot leak under the slab and your right the number one complaint is not enough hot water and number 2 hearing a noise of water running while none is being used and number 3 a hot floor or warm number 4 high utility bills. I also ask if the showerheads have been changed and flow restric taken out......thats a big reason for not enough hot water. Not paying the gas bill is another.

A cross connection will follow the path of least resistance. The more probable answer would be a cross connection not a leak under the slab and thats one of the easiest things to diagnose here and would not require a visit. Turn off the water heaters cold inlet supply stop valve.........wait a few minutes and turn it back on.......if you hear water rush in to the tank...........bad news you have a leak under the slab if no hot faucets are dripping,etc. I've had old ladies do that before and called me and told me they have a leak.........with no training....they just heard water running and turned the water heater off and then back on......heard it re-pressurize. Some people still have common sense.



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You are right Britt. I know I don't have a slab leak because I have no plumbing in the slab. Here in California we have "post tension" slabs that have cables running through them for strength during earthquakes. These cables are under tension and the slab could explode if cut into. For that reason, my builder elected to put all water lines above grade. I think my hot water problem is a cross connect in one of the shower valves. If you or anyone reading this knows how to remove the decorative backing cover on a Price Phisher single handle shower fixture, I'd appreciate some suggestions. I took the handle off, but there is a small trim piece that is holding the backing cover on. It looks like it might take a special tool to remove. Anyone? Thanks, John

Shouldn't need a special tool. No screws heh? Its gotta have some type of trim ring that screws off. it maybe just stuck on there with silicone. Dont do anything until you find out for sure. maybe call p-p and tell them the year it was installed and they might can send some info or go to your local plumbing repair parts specialty store with the handle and ask about the trim removel.

well then there you go. you just solved your own problem. it is the water lines running up the outer wall into and through the attic being heated by the extreme temps up there.

i bet you do have lines under your slab. we use the same type here and they always have plumbing under them.

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The guy has been living there for 7 years. I'm sure his pipes were in the attic last year too and the year before that. The problem has just recently started.

and isnt CA. in the middle of record breaking heat?

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It only takes 1 degree to break a record. Its damn hot this year and last year and the ones before that. Those guys up north have no idea what we go through down here. It doesn't stay hot up there for aslong.

What happened to turning off the re-circ to see if that's the problem? Just unplug the pump. If it's hard-wired and there aren't any valves, it's installed incorrectly (you couldn't replace the pump w/o turning off everything). It may be a bad check valve on the return.

Here, the plumbers working on posttensioned slabs use PEX so they put it overhead anyway. The attic can heat the water well beyond, or at least very close to, 120 degrees.

One of the problems with trying to diagnose something like this remotely is that we don't know anything about his system. For example, his recirculator might be a Grundfos Comfort system with a bad control valve sending hot water into the cold system back to the tank, or a bad single handle faucet but that is unlikely, (cold water in the hot side would be a more common problem with this situation), or something completely off the wall that we would have to be there to see exactly how his piping is done.

Thanks for all the replies guys. I took a picture of the recirc system. It is a Taco brand. Also, there is a couple of pictures of the shower fixture I am trying to take the trim ring off of.

Note: I did unplug the recirc pump and yes, the problem stopped. But what does that tell me? If I have a bad fixture mixing valve it would only leak when hot water is flowing thru the lines, correct?

Here are the pictures: [good-times.webshots.com]

Scroll down below pictures for comments



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your check valve is in the wrong spot and is most likely the cause. it should be on the in coming cold water line because when the pump is running it can over power the cold pressure and the check valve is supposed to stop that from happening but where yours is it is impossible.

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When the recirc is running, water is flowing in a loop to (presumably) the furthest fixture then back to the water heater. This makes the hot water available w/o a long wait. Check valves do fail; sometimes the gate will get stuck open, and 7 years sounds about right. If the problem goes away when the pump is off, that's where I'd be looking.

The check valve is to prevent the cold water from flowing backwards through the pump into the hot water system. A pump creates a closed loop and it cannot circulate water through any piping not in the loop. The check valve is in the correct place, but another one could be added with limited effects.

The check valve is in the WRONG place as dlh said.

So move it and then when the customer wonders why the last fixture in the loop always has cold water, you can put it back where it is.

Your so so so lost. The pump circs the water through the loop. The loop goes from the outlet of the pump to the top of the water heaters cold side......down the dip tube and out the top of the heater. The circ return line connects at the last fixture on the hot supply line feed and returns to the pump creating a loop. The check has to be BEFORE the tee at the top of the heater. Otherwise what are you keeping from backflowing the pump is pushing the water........its not gonna backflow there. By the way i dont like the way that pump is installed I like to pipe it in at the bottom of the water heater...........if the pump runs all the time and with thin plastic dip tubes will go bad prematurly. The feed doesn't hafta go through the dip tube so why make it unless you have no choice. just my preference.



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If the check valve, located where it is, has worked just fine for 7 years, it's probably in the right place. If the problem goes away with the pump off, I'd take a look at it. I'd probably just replace it & would be surprised if that didn't fix it, but I do get the occasional surprise.

I believe the check valve is in the correct place, as it prevents cold water from flowing into the hot line when the pump is not operating (it shuts off from 10pm to 6 am) I would think that if the check valve was bad, my problem would be no hot water when the pump was off. What is curious to me is why there isn't a check valve on the other side of the T to keep the hot water from flowing into the cold supply line. Is it because the supply is sightly higher in pressure, or just fluid dynamics of hot vs. cold water?

Please read your posting before hitting send. When you say the check valve has to be BEFORE the tee, that is ambiguous. Do you mean between the pump and the tee, which is the correct place, or between the tee and the cold water shut-off, which is unnecessary? Both locations are "before the tee" depending on which section you are referring to. There is no "loop" between the pump and the cold water system so flow will not occur that way.

Check valves do fail, but first you have to find out if that is the problem.

It it the fluid dynamics that a pump cannot circulate water unless there is a continuous loop, (i.e., the circulation piping), to provide a path for the movement. It is the reason that retrofitted circulation systems, such as Grudfos, can use the cold water line as a path with the right controller to prevent filling the cold water pipe with hot water. But since you do not have that system, it is not the cause of your problem.

Upstream of the tee on the cod water side before the tee. Some house will have a problem if you only put one where he has it. It depends on sooooooo many things. I had a customer with all moen single lever old style faucets all 1225 cartridges. Her ballcock didn't close and the toilet ran for 6 hrs straight, when she came home te toilet as steaming with hot water. I went straight over and pulled the access off from behind the closest bathtub and the cold pipe was hot! I replace the cartridge and the problem stopped.....this was 4 or 5 years ago. It was crossing at the cartridge. No if, an's or buts about it. Even professional piping engineers differ on opinions about systems. probably because the have experienced a problem the other has not.....and its a very odd problem that doesn't happen much. Different areas of the country have used different methods of design and with all this new equipment people are installing can have conflicts when used together or is piped a particular way. Fluid dynamics hae been argued for years.

I'm just saying I would have put two. I ususally pipe the return to the bottom with a check and a check at the top on the cold side. Also circulating hot water heated over 140 degrees can cause mineral precipitation........and if the pump is over sized it will make it even worse.

if piping a recirc to the bottom of the tank why would you waste the time and money putting a check on the cold line? it is way harder for the circ pump to pump that much pressure up a little dip tube unless there was a pressure drop on the incoming water and then it would find the hot line to be a lot less resistant. now on the top installs i to would use two checks.

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Sheesh, I musta got thumped in the head with precipitating minerals!

So the problem stops when the recirculation pump turns off... What does that say??? I'll clue you in precipitating minerals has nothing to do with this...

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I had a house once that wouldn't work without it. A massive grohe shower system was also installed with a 3" drain. Every now and then they would have temp problems of hot coming out of cold faucets. We replaced everything to do with the pump twice and the check valve because it was intermittant......and the customer was weird and hardley ever there....so noway to check it out everytime it happened. I said well if the pump is causing the problem.........i will install a check at the top of the water heater also on the cold,to completely isolate the cold from the hot. This corrected the problem. i called several times to make sure........he said it was working perfectly since. the pump was a replacement of the same brand and model with identical specs to the old one. Expansion tank was working. Nothing was ever done to the shower or valves. the problem never came back after that. Later we found out the house had two meters and two seperate cold lines. One meter stayed off because it was for the boat house....but it also connected to the main house,main water feed. the maids would turned it on at a valve in the yard to clean. they would somtimes leave this valve on and thats when the problem would happen. he said the water co wouldn't give him a big meter so he installed two. he had an isolation valve to keep them seperate but the maids turned it on too! he wouldn't let me disconnect it......he said he wants all te water he can get. This fool had 3 clothes washer and 3 dishwasher all side by side. freakin mansion he sold land big orange purchased to build store and started checkers hamburger franchise then sold it. Filthy rich.

It could be the reason his check valves bad and his shower cartridge. I never said it had anything to do with it. If he would send me a check i'd go figure it our for him. Sounds like he has more time than money or he woulda called sombody anyway. Goodluck Mr hot water through cold pipes. Isolate all the hot from the cold and reconnect one by one until you find it.Start at the most likely causes. I'm done with it.

I own an apartment building in Austin, Tx. I've had a plumber spend a fortune doing everything BUT replacing the Mixet brand tub/shower valves in trying to fix a lack of hot water problem. I brought in another plumber who said my problems dictate FIRST looking at the valves to see if they're Mixet brand. If so, replace those valves to see if there is an improvement. He says that any decent plumber working on apartment buildings should know about the Mixet problem, because they are notorious for causing exactly my problem. He replaced the Mixets and now the problem is gone. However I now need to independently substantiate that the 2nd plumber is right about common knowledge about Mixets so I can show that the 1st plumber cost me a fortune by his lack of common knowledge (by the way, I learned in a subsequent meeting with that 1st plumber that they actually do very little work on apartments...but they are standing on the defense that they'd never heard anything about Mixets and their plumbing supplier would have told them if Mixets were a problem). Messy Deal...but any input on the matter and/or direction to credible sources of information would be hugely appreciated. Regards: John

re:
"Author: britt (AL)
Upstream of the tee on the cod water side before the tee. Some house will have a problem if you only put one where he has it. It depends on sooooooo many things. I had a customer with all moen single lever old style faucets all 1225 cartridges. Her ballcock didn't close and the toilet ran for 6 hrs straight, when she came home te toilet as steaming with hot water. I went straight over and pulled the access off from behind the closest bathtub and the cold pipe was hot! I replace the cartridge and the problem stopped.....this was 4 or 5 years ago. It was crossing at the cartridge. No if, an's or buts about it. Even professional piping engineers differ on opinions about systems. probably because the have experienced a problem the other has not.....and its a very odd problem that doesn't happen much."

Not sure how old this post is, but I have a similar problem with a house that apparently used to have a circulating pump, but now converted to tankless. All new fixtures, including two shower panels. Depending on how my plumber connects the old recirc line, I either get hot water on hot side of all fixtures and tepid water on cold side, or cold water on cold side and tepid water on hot side. So, there is a cross connection somewhere...but where?

The effect is pretty instantaneous. Would a bad shower mixer (with low flow output) cause enough cross-over to affect at least 100 feet of copper pipe in a few minutes time?

I also confirmed there is cross-over by turning off hot water supply line. All fixtures in the house ran cold, with full pressure from both hot and cold sides of faucets. This included two bath tubs with dual/separate hot/cold valves--not single lever mixers, like the shower panels and bath sinks.

Not easy to remove the shower panels, as they are somewhat fixed in place in the tile surround. I listened with stephoscope, and could hear water running behind the handle, but all the fixtures were pretty much transmitting some sound. But, there was less sound at the shower than at the two separate lines at the tub faucets

It definitely appears there is a physical cross-over, but seems like it is downstream of where what appears to be the recirc return line comes back to where the old tank water heater used to be.

Any insights you or others might offer would be helpful.