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Question DetailsAsked on 6/8/2017

dripping sound only when using hot water in the bathroom

Starts out every 2 seconds then slowly diminishes no leaks seen. isn't from cold pipes doesn't get cold here 60 degrees. I am a DIY put in a toilet and sink and floors. is like a hollow drip sound. mostly when turning faucets high.(hot) Comes from seems like behind wall. Maybe 4 ft away I don't think is a water leak cause it would drip more w/ faucets are off right? due to more pressure? I also did some drywall repairs due to mold. was causing the wall not to sit square so I moved a mounting bracket for the pipes to sit recessed on the wall stud instead of over the stud only maybe 1/8 inch or so inward.(is still not square but is behind the vanity)
Thank you for your assistance

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2 Answers


That sound, especially with no sign of water damasge over time, is typical of thermal expansion/contraction. Rarely occurs with cold water pipes and if so almost always only when the water is first running (meaning you would not normally notice the sound in the bathroom where the water is being run).

Hot pipes commonly do this - and while copper or galvanized will do it (usually only in tight-fitting holes through joists and plates), hard plastic pipe (PVC or CPVC water or PVC/ABS drain pipe) is especially prone to it even if just laying on blocking or in a large size hole. Sometimes (especially in downstairs rooms with water pipes in the ceiling) you can hear the expansion, but the typical complaint is a popping, tapping, dripping, or creaking sound at typically a second or two interval after the hot water flow is shut off, tapering off to longer and longer interval, and commonly lasting 15-60 seconds before it tapers of completely.

A key to this versus a leak drip sound is the tapering off of frequency in the minute or so after the water stops running and lack of any water staining. You can commonly also change the frequency or stop it entirely by pushing /pulling on the pipes under the sink (not hard enough to break them), and also by running the hot water just a bit to keep the pipe at the same temperature - so say it normally happens for 30 seconds, if you run the hot water a steady slow flow (slow enough to be quiet) it will usually stop the drip/tap sound within a couple of seconds.

Here is a previous similar question about this mystery noise with a lot of back and forth and responses explaining in more detail, ,and also talking about how to stop the sound:

Answered 3 years ago by LCD


My house is 16 yrs old. After using the hot water in the bathroom sink only upstairs, I can hear some kind of water dripping sound from the first floor ceiling (near the corner of the living room and garage on the other side of the wall). It will last about 2 mins and then stop and only happens after the hot water has been turned off from the sink. It doesn't happen with the shower or toilet. I have checked around the ceiling, walls and garage, but see no sign of water leak. How can I stop this dripping? Or it is just a matter of fact that the PVC pipe is expanding and contracting when the hot water go through it and I can't do anything about it.

Any help would be appreciated.

Answered 2 years ago by CatRun

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