Hello. My subject line pretty much explains it. It was first noticed after we had to replace a faulty valve in the dishwasher that controls the water flow. It was stuck open. Around that same time I replaced a fill valve on my toilet, about the only thing I'm good at. : ) I'm about to drain my hot water heater but I don't think that's it. And the temp isn't too high, but I did lower it after hearing the hissing. It may have been slightly high.

The three locations are:

1- Very faint sound coming out of the hot water tank (only noticed that today after a few weeks after hearing it near the DW
2- A little more present behind the basement shower at a connection just prior to it going under the slab
Near dishwasher at shut off valve. It's the loudest at this location. This is the same bathroom where I replaced the fill valve in the toilet.
3- Very noticeable at the shut off valve feeding the dishwasher. If you didn't know better you'd think there was air coming out of it.

Yes, After my piping leaves our downstairs it goes into the slab on the way to the kitchen. Any help would be great. The plumber we had out to do some other things didn't really know how to problem solve this so I'm trying to educate myself more before calling out an expert that deals with slabs.

Last night I turned off the water heater and cut off the hot water supply leaving the hot water tank. This morning I turned it back on. Then a little later I opened up the valve on the HWH. The hissing turned into a pulsating hiss until I opened up a few hot water faucets and then the normal hiss came back. Any guidance would be great. I'd like to shut off the hot water supply at the tank unless turning that on and off could back a possible leak in a pipe under the slab get worse before I get someone out here.

With a slab leak sometimes the best solution is to abandon the piping in the slab. New PEX is ran through the attic space and down walls. The piping in the attic should be insulated to protect against freezing.
I have personally been involved in this as an apprentice. But as a plumbing contractor I do not go into attic spaces unless I'm really looking for work and kind of desperate

From your description, it appears you have leaking hot water line.
1. Call a leak locator specialist to determine where it
2. call your homeowner's insurance company and tell them what happened and submit aclaim
3. If they do not recommend a plumber, call one to repair the pipe
4. Plumber will access the pipe as part of the claim
5.Plumber will repair the leak. NO part of the claim
6. "someone" will make the repairs to the building as part of the claim.

The first thing to figure out is what the hot line under slab is feeding by installing a shut off valve on that particular line, when the new valve is installed and in the off position open the hot side of all suspected faucets, once the fixtures are determined you will decide to either break up the floor under the kitchen sink (or dishwasher if it’s a separate line) or like posted above run a new line in the attic or another feasible area… a true plumber will be able to guide you in the best direction, maybe try calling another plumber with more experience or try a leak detection company

Good luck

Thank you. Appreciate the feedback.

Thank you very much. That sounds like the right plan. I was hoping since I didn't see a change in my water meter that maybe it was a pressure thing. It's hard to check the water meter after 8 or more hours because someone is bound to use some water.

Thanks. Appreciate it. All of this is great information!

....and There's just one line that goes under the slab as it leaves the downstairs. We have a split level and one side of the house is on the slab and only the kitchen has water on that side of the house. Thanks for taking the time to reply.

With the noise much less now that I have only cold water in my hot water heater does that open the possiblity that maybe it's not a leak and has something to do with the hot water heater? Wishful thinking?

If your water lines are copper, replace them with PEX and sleep at night.

I think there's a fix that has you sending a smaller pex line through the copper line, but you do lose some pressure.

YOu should be able to tell almost immediately by observing the small red star flow indicator in the meter. Without being there wE are relying on your observation. To verify the problem a GOOD plumber should check it first.

Thanks for that. I misunderstood what my wife said she checked with the plumber. I thought they were looking at the numbers like I was. Ya, it's not spinning at all. I put the slowest possible drip I could from my kitchen sink and it was spinning. Interesting. Learn something new every day. Thank you.

if the water meter is not spinning you have no leak in the lines.

now if it is spinning when no one is actively using water in the house, then you MAY have a leak, but it could also be something else consuming water that is not an actual leak. For example, you may have no one using water at that moment, but the refrigerator icemaker may be pulling water quietly while making new ice, or could be you have a faulty toilet tank flapper and water is seeping through and triggering the fill valve to refill periodically, will both cause the meter to spin while no one is "using" any water.

How is the water heater's temperature and pressure relief valve behaving?

Thanks. Well, I "flushed" the hot water heater somewhat, reset the temp to read out at 120 at the furtherst faucet and the hissing in the shut off valve in the kitchen get much more quiet. One test I did. I noticed the HWH turns on about the same time each early morning. Last night I turned off the water leaving the tank and it didn't turn on. Now it was 35 degrees one morning and 45 the next when it turned on and it's in a room with an outside wall with a door that is drafty. I was testing to see if there is a pin hole leak in the hot water pipe somewhere it may drain enough to cause the HWH to kick on. When I cut turn of the hot water supply leaving the tank all hissing stops. The hissing when I open that line back up turns into a pulsing type of hiss until I open up some faucets. Tonight the hissing at the shuf off valve on the hot water line is not there. No hissing at the water line leaving the tank. I haven't re-checked the flow indicator but it hasn't been moving unless we open a faucet. Sorry I was MIA, busy work week. I so appreciate everyone's feedback as I cannot decide what company to hire to come out. I do have a annual service warranty on the hot water heater and think I'll have them come out. It seems like nowadays customers like me have to do a ton of research and then suggest what might be wrong.



Edited 2 times.

I wish I knew how to reply to everyone. Well finally I see the flow indicator moving and I'm trying to get someone out here. It's hard to find a leak detector specialist and slab specialist. I am stopping the leak by turning off the hot water supply from the hot water heater. I've done that a few times and notice the leak could be getting worse. Am I straining it by opening and closing the valve? If anyone reading this reply knows of a great person or company in the fairfax county/Northern VA area a recommendation would be greatly appreciated. Thanks.

As stated in earlier posts the old line can most likely be abandoned and a new line run from above or through the kick space behind the cabinets or exposed inside the bottom cabinets and strapped to the back of the cabinets(running a new line if usually easier both in work and your wallet