Warm water from every cold tap

[Heisenberg]

I own a single family home on public water and have lived here for two years. The cold water used to run fairly cold, but one day a week ago after using the shower we noticed that the cold taps were running lukewarm from every faucet. I experimented with shutting off the water heater intake pipe and the main intake line, and after fiddling around with it grumpily for a half hour or so it seemed to go away. Today the incident returned and I can't get rid of it.

I researched the problem and it seems like the issue is most likely a "cross connection" between the hot and cold water pipes. The most common place for such a cross connection to occur seems to be cartridges in single-lever faucets. This would have made sense to me, since not only do I have three single-lever sinks and two single-lever shower faucets (all Delta as far as I can tell), I also had some issues with one of the shower cartridges when I first moved in--it was installed backwards, so hot and cold water were switched. I fixed that myself months ago and had no issues afterward.

I figured that cartridge or another one had gone bad. So I turned off both hot and cold taps at all five faucets, showers (behind the faceplate) and sinks (under the sinks). If I'm understanding this correctly, stopping the water at these points would prevent it from "crossing over" and mixing at the cartridge. However, no such luck. I tried turning back on one sink at a time and testing it. Each sink still runs lukewarm water from the cold tap even with every other single-lever faucet in the house turned off.

My understanding is that the only other point the water could really be mixing is if hot water rises up the water heater intake pipe due to convection. So at this point I also turned off the intake pipe to the hot water heater. The hot water taps, as expected, all cease to work when this pipe is turned. Amazingly, though, the cold water taps continue to deliver warm water! I wouldn't have thought that possible!

I don't believe the pipes are actually crossed anywhere (e.g. cold water pipe to hot water tap) or anything like that. As I said, everything was functioning fine until recently, so I have to believe this is a recent failure somewhere in the system. Aside from flipping the cartridge in one of the shower faucets, which was months ago, no other plumbing changes have taken place in two years. We have been running the dishwasher more frequently after rarely using it the first year or so, but I wouldn't think that could be the issue.

What the heck is going on? Am I correct in ruling out the faucet cartridges as the culprit or is there something I'm missing there? Could water still be backflowing up the water heater intake pipe even while the pipe is shut off? Should I call the water utility? Call a plumber? Call the exorcist? Help!

 

[johnjh2o]

Do you have a recirculating hot water system? There are two types one is with a dedicated return line the other one uses the cold water line.

 

[Heisenberg]

Do you have a recirculating hot water system? There are two types one is with a dedicated return line the other one uses the cold water line.

Not as far as I can tell. How would I know for sure? Everything seems pretty simple and straightforward. I can pretty much visually track all the plumbing as it's run through the ceiling of an unfinished basement. There's just a cold line, a hot line, and the larger waste lines.

 

[johnjh2o]

A dedicated line would be a third line connecting at the heater in most cases at the bottom of the heater. The type that uses the cold line would have a fitting connecting the hot and cold under the sink that is the farthest away from the heater. In some rare cases I have seen the clothes washer hookup cause a cross connection. You said you turned off the water behind the face plate of the shower valve. Are you sure the stops for the shower are holding?

 

[IPLUMB]

I have seen a aftermarket Non Moen tub/shower cartridge cause this. It was in a Moen Posi temp. The 1222 cart.

 

[Heisenberg]

A dedicated line would be a third line connecting at the heater in most cases at the bottom of the heater. The type that uses the cold line would have a fitting connecting the hot and cold under the sink that is the farthest away from the heater.

There is no third dedicated line at the heater or anything connecting the hot and cold under any sink. Nothing under any of the sinks except a disposal unit and gray dishwasher hose hookup under the kitchen sink. So seems like no recirculating system.

In some rare cases I have seen the clothes washer hookup cause a cross connection.

The clothes washer hookup is always closed off, both taps. Has been for months. We don't use the washer or dryer.

You said you turned off the water behind the face plate of the shower valve. Are you sure the stops for the shower are holding?

I turned the two screws in the fixture behind the faceplate to stop both cold and water taps. I tested the faucet afterward and no water comes out so I assume they're holding. Is there another way to know for sure?

I have seen a aftermarket Non Moen tub/shower cartridge cause this. It was in a Moen Posi temp. The 1222 cart.

Both shower fixtures and bathroom faucet fixtures are definitely Delta. Not sure what the kitchen sink is or if the individual cartridges are aftermarket or off-brand?

I left the water heater intake pipe and all the faucets except one shut off all night long. This morning the water ran cold for a little while but became lukewarm within a few minutes.

Also, I noticed the water heater intake pipe is warm to the touch. It's very warm at the base of the pipe, closest to the heater, but even higher up the pipe it's still not cool as I would expect.

I almost feel like the stop for the water heater intake pipe has failed, but if that were the case wouldn't the hot water taps still run even when the pipe is "shut"? They don't; when I close the water heater intake pipe, the hot water taps stop more or less as you would expect. (There is some continued dripping from one of the bathroom faucets if the faucet is left on all the way hot even when the intake pipe is closed. Could that be indicative of an issue?)

At this point the only thing I can think of is to try to install some kind of check valve or anti-backflow valve where the sealed copper part of the water heater intake pipe meets the PVC piping...

 

[johnjh2o]

What your describing makes no sense. You cant have hot water mixing with the cold if you have turned of the hot water source. There is something missing here. At this point without being able to look over what you have it's impossible to identify the cause.

 

[Heisenberg]

What your describing makes no sense. You cant have hot water mixing with the cold if you have turned of the hot water source.

I agree it makes no sense and would have thought it impossible for hot water to be in the line if the water heater intake pipe is closed, but somehow it's happening. Thanks for helping anyway.

 

[Heisenberg]

Just to double-check, today I once again shut off every hot/cold tap at every fixture. I even took the cartridges out of the shower fixtures completely. I also shut the water heater intake pipe off. I tested the water at the external garden hose--still lukewarm.

I think I can draw some conclusions from this. I seriously doubt it's a cartridge issue in one of the single-lever faucets since they are all shut off completely; the water lines aren't meeting there to mix. The only other logical place it could be crossing over would be at the water heater piping itself. Turning off the water heater intake pipe prevents any water from coming out of the hot water taps, which leads me to believe the intake pipe valve is functioning correctly; however, since shutting off the intake pipe valve does NOT reduce the warm water in the cold line whatsoever, that means either 1) the intake pipe shutoff valve actually IS defective, possibly causing this whole problem, or 2) the shutoff valve by design doesn't prevent hot water from returning up the cold water intake pipe.

Since this is a new problem, I also believe something has failed recently or is beginning to fail. Taken all together, to me this implies one of two things: 1) some mechanism that prevents backflow, e.g. a dielectric heat trap, has recently failed OR 2) the thermostat in the water heater has failed, causing the unit to continuously work and "super-heat" the water, causing a recent increase in convection, thus driving more warm water into the cold line. (I can't tell if the hot water tap, when running, is hotter than usual or not--it may be, which would support this theory.)

I also found this:

http://www.amazon.com/dp/B0006JLVEE/?tag=skimlinks_replacement-20

I wonder if something like this might be installed in the pipes and recently have failed? Regardless, would installing something like this be likely to help this problem if it is indeed hot water backflowing from the water heater?

The only other completely outlandish possibility I can think of is that lukewarm water is coming in from the main line! Tonight I shut off the water heater intake pipe, turned off the water heater at the breaker box, and ran the water at a faucet for a good half hour to try to drain the hot/warm water out of the system. I'll leave it like this overnight and then check in the morning. I figure this way I can at least confirm for sure that it's my water heater that's contributing the hot water to the system.

 

[johnjh2o]

The fact that your missing is if there is no water entering the heater none can leave the heater. Even if the valve has failed there has to be a cross connection to mix the hot and cold water. To check if the valve is holding turn it off then open a hot water faucet, place your hand on the hot water line were it exits the tank. If the valve isn't holding that line will become hotter.