Just recently started getting warm water from the cold side of my faucets. Doing some research, I saw that a big culprit could be water-mixing valves on washing machines and single-handle faucets. Well I don't have any single-handle faucets and I keep the water shut off from the washer until I get ready to use it, and I only use cold water when I do.

I also read about thermal expansion and open vs. closed systems. I am on a well and a septic tank, which I assume is an open system. There are no check valves or pressure reducing valves installed where the supply enters the house. Don't think there is any in the well either. I did see that thermal expansion can occur in an open system, though more likely in a closed system.

The water heater was replaced last year, but on this heater as well as the last one, the fitting on the cold inlet to the unit always felt warm, sometimes hot. I have checked the T&P valve on the unit, and I get hot water out of it when I open it up. The valve has never opened up on its own, it has never been "tripped".

So my question is, am I dealing with thermal expansion or is there something bad or going bad in the heater itself? The way the piping is run, there isn't a drop on the pipe that would help with thermal expansion. Should I get a plumber out to put a drop loop in the piping (PVC) or get an expansion tank installed? I should also mention that I drained a gallon of water from it, and the water was very clear, no sediment. And if I run hot water, the cold inlet pipe is cool to the touch, but then when I turn on the cold side, it starts cold and gradually gets warmer, lukewarm not hot.

Your advice is greatly appreciated.

What is the water temperature of your well water? Maybe you do need some check valves in your cold water inlet to the WH if it is the same feed line to the WH and house cold water. Turn the water heater off and see if the problem persists.

Is your plumbing in the attic? I have a 225 ft. well with 150 ft. of poly pipe. My water is so cold, it hits the HW heater pretty good. Not sure how your house is plumbed but sounds like some type of cross connection. I ran 3/4" CPVC throughout with 1/2" risers. 2 single handle tub faucets. Never had an issue.

Thanks for the responses. I don't know what the temp of the well water is, but it has been hotter than the door handle to Hell here the past week.

The plumbing is not in the attic, it is in the crawlspace. The main line comes in under the house and branches off to feed the bathroom sink, toilet and shower and to the kitchen. There is a utility room on the other side if the kitchen wall where the supply lines come up to the sink. There is a feeder line that comes off the cold supply to the kitchen sink that goes to the WH inlet, with a shut-off valve on it. The hot water pipe comes off the WH and feeds to the sink and then off to the bath sink and shower.

I have noticed the problem occurs only after I use hot water. Turning on the cold without having used any hot, the water is cold. I washed dishes using hot water and then was going to fill a pitcher with cold water to give the dog. Normally, it takes about 2-3 seconds for the water to get cold, but the water never got cold. Didn't stay hot, but got lukewarm. Ran a little over a gallon and it never got cold. After a few hours, the water is again cold and stays that way until I use more hot water.

This has never been a problem before, and no plumbing work has been done in a long time, so it couldn't be a cross connection could it?

My main concern is that is thermal expansion and fear that the thing could explode and go through the roof like a rocket.

"Ran a little over a gallon" That's not a whole lot of water, considering ambient temp, to cool down. Run it longer and check. If the TPV valve functioned manually, it should do so in practice so I wouldn't expect it to blow. If you are on a well, you don't need an expansion tank, the well tank operates as such. If you are on city water and they have backflow valves, our county has them, you do need an expansion tank.

, mine sits directly above the HW heater.

I would be interested to see what your house pressure is.

Thanks ma0641. I am on a well, so that makes me feel better, and knowing the TPV works manually. If the pressure did get too high, I would think that there would be some signs, such as some very strange noises coming from it. I have never checked the water pressure, but the well switch is set at 30/50. The pressure has always been good, not too high or low, with the exception of the shower, which greatly improved when I switched to a Delta H20Kinetic showerhead. The WH is set at about 135 degrees, and I've seen 130 as the most recommended. As far as the water pressure goes, how would that contribute to the problem, if it were too high or too low? I'll check that, but I need to get a proper gauge to do it.

Is your shower valve a single handle? If so, then that is the most likely culprit... just change out the cartridge and should be all set. If you have a two or three handle shower valve then issue is definitely elsewhere.

Foot valve at well acts as a check valve on well pipe so expansion problem unlikely UNLESS something stuck in the foot valve and then that could cause some back siphoning, I suppose.

No need for expansion tank or "drop loop" if the T&P valve has never dripped by itself.

Let me know more...

Mark

Thanks Mark. I have a three handle valve in the shower, don't have any single handle faucets, so it is elsewhere. Where is the big question.

Does the same happen during cold months ?

Just a thought: It is very possibly your cold water pipe produces warm water because of the high temperatures outside. It happens in my house 8 months of the year.

Milo