Cold water is hot due to amateur plumbing

steam-rookie · May 3

the hot water tank in the photo is being used for storage only. The coil in the boiler still works, and produces plenty of hot water. All of a sudden, out of nowhere, the cold water is mixing with the hot water. I am getting hot water from all of the cold water taps

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in the house.The current set up has been like that for many years. I have been told on numerous occasions that the pump is in the wrong place. I have been told it should be on the top somewhere.
so, looking at the photos. Can anyone tell what is wrong and why I am getting mixing with the Hot Water into the cold taps.

EdTheHeaterMan · May 3

Check valve missing

Screenshot 2025-05-03 at 10.38.44 AM.png

neilc · May 3

~~is the recirc running?~~

~~does it have a check?~~

~~and or is it stuck open?~~

yeah, nevermind, still need a check on the cold supply to the domestic hot

Mad Dog_2 · May 3

You have a cross-connection somewhere. The usual suspects...

Single handle mixing valves like shower bodies, Washing Machine valves.
Mop Sink connections that are altered.
Domestic hot water coils using a globe valve to blend.

Yes, you also may need a check valve, but when this condition "suddenly" occurs, it's usually at the aforementioned locations. Mad Dog

EBEBRATT-Ed · May 3

Agree with @Mad Dog_2 if the problem just started a check valve may not be the fix.

steam-rookie · May 3

thank you for the quick reply.

There used to be a check valve just after the pump where the red valve is located. It caused a lot of water hammer when the washer went on, so I took it off. The only other thing that has changed that I think of is that the heat is off. Anyway, I think installing a check valve at the new suggested location looks like something I could try. I like that idea because it’s way closer to where it seems like it’s mixing to me.
that pipe coming down should be ice cold. It’s pretty much hot all the way up now. Maybe placing the check valve there might be a really good idea.

hopefully when we run the washing machine there won’t be a lot of banging

neilc · May 3

if you innstall the check on the feed to the DHW, you might / will need an expansion tank on the hot side since the DHW will be isolated from expanding back to the house side,

and what Ed Mad Dog says, Cross Connections ?

mattmia2 · May 3

https://forum.heatinghelp.com/discussion/comment/1854412#Comment_1854412

I was about to say that then looked at it more closely and i think the check is just on the bypass, the dhw system is still open to the cold water inlet through the coil.

steam-rookie · May 3

I believe that the last comment made is correct.
The check valve should be on that cold water inlet.

if it starts to have water hammer I also agree about the expansion tank. There has never been an expansion tank anywhere

That will be my next question without a doubt.

Larry Weingarten · May 3

Hi, If you put a check inline before the water heater, thermal expansion will have no place to go, so will raise pressure until the relief valve lets go. So, an expansion tank is needed if a check is put upstream of the water heater.

I'll add that the test for cross connection is pretty easy. Just turn off the cold supply to the heater and open a hot tap. Water should stop flowing in seconds. If it keeps running, you get to hunt down that cross over. 🤠

Yours, Larry

EdTheHeaterMan · May 4

I also agree that using the check valve will require an expansion tank like this one: https://www.supplyhouse.com/Amtrol-140N43-THERM-X-TROL-ST-5-Expansion-Tank-3714000-p

steam-rookie · May 6

thank you for the replies.
this plumbing set up has been running without any issues for over 30 years

Nothing has been changed. This problem seems to have coincided with the thermostat, no longer calling for heat in the house. The weather has gotten warmer in New York.

I felt the cold pipe leading into the boiler. It was hot. As a matter of fact, I continued upstream and still hot. I followed the pipe around the basement and everywhere it should’ve been cold it was hot. It finally felt cold Just before the meter where it comes in from the street.
One thing I did notice is the pump seems to be running much more than usual. During the winter, it hardly turned on at all. But now, every time I go down into the basement that pump is on.
so, instead of pumping the water into the coil. It seems to be pumping the water back up into the cold supply.

Maybe the coil got clogged up. I don’t know. About the cross connection discussion. I don’t think a cross connection is possible because I haven’t done anything to the plumbing. Please let me know if I’m wrong about that. Do cross connections just happen on their own.

here is some more info.
The hot water in this house comes from the coil in the boiler. The pump pushes water from the tank into the coil and then back out from the coil into the tank. There is nothing heating up in the hot water heater. It is a storage tank only.

The system has three thermostats.
There is one on the boiler. And there is two in the hot water tank. They are all active. The thermostats top and bottom in the hot water tank turn on the pump.
like I mentioned before, this system has been working very well for many years.

Sometimes, I could feel the hot water creeping up that cold supply pipe. But would only get about a hands length and then the pipe would be cold again.
In other words, there has always been some mixing without the check valve. But it has been extremely minimal. Maybe 6 inches or so up the pipe. currently that 6 inches has turned into the entire cold water supply all the way to where it comes in from the street.

This situation, to say the least, has been very alarming. And, I don’t know what to do about it. Frustrating.

The only other thought that I have is this:

is it possible that because the boiler is not turning on as often as it did in the winter. Would it be possible that the thermostats in the tank are set to high thus causing the pump to stay on much longer than it used to

I did not explain that well, but I have a feeling that the thermostats in the tank are not in alignment with the thermostat on the boiler.
That would explain why the pump is constantly running. And maybe explain why the hot water is backing up into the cold water system. it’s possible that the coil maybe can’t handle the pump being on for that long.

Does this sound reasonable to anyone.

steam-rookie · May 6

I have another question.

is it even possible that the little pump could overcome the water pressure that comes in from the street.

Larry Weingarten · May 6

Hi, Just to address one point, cross connections can happen simply from hard water changing the way seals seal. I'd do that test so the possibility can be ruled out.

Your, Larry

Big Ed_4 · May 6

The check was used on an aqua-booster to direct the incoming cold water though the coil to help keep it clear. But it will drop the pressure ….

You have a bypass ……. Shut off the hot water and then open a hot facet , if water runs out , then you have a bypass …

Hope this helps

steam-rookie · May 10

thank you

By looking at the photos what valves would I turn to shut off the hot water. I would like to try the bypass test.

steam-rookie · May 13

IMG_1649.jpeg

I am really hoping to perform the for mentioned test. By looking at the photo, would this be the correct valve to turn off the hot water?

Larry Weingarten · May 13

Hi and yes, That looks like the cold supply to the tank. Also, is that romex carrying 120 or 240 volts? If so, I'd put it in conduit 😉 I'll add, just to prevent confusion, shut off the red handled ball valve on the line from the boiler for this test, and turn off power to the pump. A thought. If there is any way that drawing hot water could cause water to flow backwards from tank bottom into boiler coil, a spring check wants to go there.

Yours, Larry

steam-rookie · May 14

thank you Larry

Just to be clear, I have posted another photo for you to look at. There are two red handled ball valves. Can you look at the photo and tell me which one.

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Larry Weingarten · May 14

Hi @steam-rookie , It's the lower ball valve I'd close for the crossover test. 👍️

Yours, Larry

Big Ed_4 · May 14

What might help you to find the location of your problem , you can feel the valve bodies , facets and washer machine connection or follow the heat migration …

steam-rookie · May 15

That you everyone.
Larry, I will use the lower for the test. The yellow piece of Romex going to the pump is 110 volts.
that is a stock electric water heater 50 gallons off the shelf at Home Depot.
I disconnected the heating elements, and left the thermostats active. It has been rewired that way, so that the tank thermostats trip on the pump.
Both pipes on the top of the water tank are hot . Everything going into the water tank and coming out it is hot . It’s just a big loop running through the coil.
The only cold pipe is the one with the red ball valve on top. That pipe is the cold water from the street.
I am going to wait until you read this in case you change your answer about which ball valve to turn.

mattmia2 · May 15

i would say the on top but it wouldn't hurt to close both as long as you turn the circulator off

Larry Weingarten · May 15

Hi, Perhaps a simpler approach is to close the upper red ball valve, as that should stop any cold water from getting into the DHW system. Then hook up a hose, or run water from either boiler drain valve ( by the bottom of the tank, or the valve above the pump) and see if pressure falls off quickly. If not, there's a crossover.
Yours, Larry

Ps. It would be good to slide some flex conduit over that wire 😉

Cold water is hot due to amateur plumbing

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