I have a water leak (I think) but no water leak anywhere in my condo. I heard the hissing noise a week ago and still no water anywhere. My condo is upstairs and my garage (and neighbor garage) below. I've been here for about 20 years and water leaks started to happen about 10 years ago. It was really annoying ... I would get one every 6 months but being upstairs mean the leaks where on the garage ceiling and walls. Easy for me to fix...so I did several times (copper pipes and solder). Then the Home Owners Association (HOA) had a company add something to the water supply and the leaks stopped. It's been about 5 years since I've had a leak. Now I hear the hissing sound. I shut off the water to the water heater and still there. If I close the main shut off valve the sound stops after about a minute. This is why I figure I have a leak...probably underground.

I hear the noise loudest from the area of the water heater. I've ruled out the water heater pilot noise and the fluorescent lamp buzzing.

The picture with the vacuum is from 15 years ago when I change the water heater and I installed a bypass for the cold water line. The bypass goes from a little below the main supply in point to a little below the cold water valve for the washing machine. The blue line shows how it is. There was low pressure for the cold water line when using the washing machine ...it used to take forever to fill. The bypass fixed that. The cold supply keeps going up to the ceiling where it goes to several places in my condo.

The bypassed line (3/4 in) still goes underground. I didn't see a reason back then to cut and cap it. There are two pipes that go underground next to the water heater discharge pipe (there are two more to the left but I think those are the hot water). A 1/2 in and a 3/4 in. I'm thinking of cutting the 3/4 in pipe and cap it first and see if the hissing sound goes away. But this only makes sense if the hissing sound of water is the source point of the leak?

The leak could be the 1/2 in pipe. I'll have to bypass/cut/cap it ... a bit more work. Then I'll be out of ideas. So before I start tearing dry wall out ... any chance the hissing sound is not where the leak is?

Thanks Pipes behind water heater Main supply outside and water heater discharge This is now

  • Might be possible to narrow down the source/location of the hiss by using a wooden broom handle(or something similar) held to your ear, and placed along the cement/floor.
    – crip659
    Commented Dec 7, 2021 at 16:36
  • 1
    If the hissing sound is coming from the water heater, I would check the pressure release valve for the source of the sound. Do you have the temperature set to high on the water heater? If possible, when it is hissing, open up a hot water faucet and see if the hissing stop. Commented Dec 7, 2021 at 16:58
  • @crip659: Interesting. I'll give that a try later today.
    – Rodo
    Commented Dec 7, 2021 at 17:01
  • @Programmer66: The temp is set very low. I'll check the release valve though.
    – Rodo
    Commented Dec 7, 2021 at 17:02
  • @Programmer66, good idea -- I've used plastic tubing as a "stethoscope" to find exhaust system leaks. (Definitely, I did not want to put my ear near the hot exhaust manifold!) Commented Dec 7, 2021 at 22:18

1 Answer 1


It's been a while since this happened but I wanted to update with an answer because the leak eventually showed up below the green arrow head (see picture in post). In the cement wall. The source of the hissing was not the source of the leak. The hissing was coming from the main shut off valve telling me that there was some "water being used". This of course was the leak. So in my case the answer was no. The hissing sound was not the source of the leak.

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