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Packerman 02-04-2011 12:48 PM

Unusual Leak Issue
In our upstairs bath room on the sink only. We have an unusual situation. Here it is:
When the cold water is running you do not hear the leak in any situation.
When hot water is run you hear a drip in two locations behind the wall. I tried plugging the drain to see if it is the supply side. It does not make the sound while the sink is filling only when it is draining. It is a steady leaking sound but we have not noticed any water coming through anywhere. I even tore out the wall behind the sink and it appears dry with no signs of leakage. Could it be the sound of dripping contained within the pipe itself? If so why would this occur with hot water only? Has anyone had any experience like this?

Jackofall1 02-04-2011 02:25 PM

Its more than likely the plastic piping expanding against the wall. The dripping sound is the pipe expanding through a hole.


plumberinlaw 02-05-2011 09:39 AM

ditto, Thermal expansion

Homerepairguy 02-05-2011 11:53 AM


Out of curiosity, do you have pex water lines?

Packerman 02-24-2011 01:47 PM

What are PEX lines?
I do not know if I do

Packerman 02-24-2011 01:50 PM

I have tried opening the wall and bracing the pipe w/ a shim but it does not seem to help. Why is it only a problem in one area of the house? Why does the noise sound like it is coming from numerous locations even above the drain in the vent pipe? Why does it occur only with hot water?

Packerman 02-24-2011 01:54 PM

PEX Answer
No I do not have PEX lines. Would they help? Are they better. What I have is black plastic pipe. I am unsure what they are made out of.

the_man 02-24-2011 02:06 PM

now that you have the wall open, do you see anything leaking? the only black plastic pipes i know of are polybutylene and polyethylene. PE is only for underground, and PB is just plain bad. What do the joints look like? can you get a picture for us?

Homerepairguy 02-24-2011 02:53 PM


Originally Posted by Packerman (Post 597218)
No I do not have PEX lines. Would they help? Are they better. What I have is black plastic pipe. I am unsure what they are made out of.

Was curious if you have PEX water lines since PEX expands/contracts quite a bit due to temperature change like a hot water line going from cold to hot. Since you don't have PEX lines, my question is not applicable.

Also, in re-reading your initial post, you said that the drip noise only happens when the sink is draining but never when filling. So the drip sound only happens when using hot water and the sink is draining. What happens if you fill the sink with hot water, then stop the filling. When only draining the hot water in the sink, does the drip noise still happen?

Packerman 02-24-2011 03:14 PM

I tried that
Yes, it does. This is how I narrowed it down to the drain. I filled the sink with hot water. I then turned the water off. It did not make the noise until I let the water down the drain.

I was wondering if a couple expansion joints in the drain pipe would relieve the tension and stop the noise. The pipe is solid with no expansion joints. I am thinking this keeps the pipes stressed.

I appreciate your help. Thank you.

plumberinlaw 02-25-2011 09:39 PM

you might be talking about ABS drain lines they are black either 11/2 or2" mine make noise with hot water also.

Packerman 03-01-2011 09:02 AM

Can this be fixed without replacing them. I am thinking that the noise would become an issue when I sell the house. It sounds like a leak but it is not. Would it help to put. Would it help if I put something in the pipe to dampen this vibration. The pipe is one solid stiff unit and any vibration goes through the whole wall.

boman47k 03-01-2011 09:48 AM

Thermal expansion

Is this causing the pipe to hit the wall studs, or is it just the pipe expanding and contracting?

If it is expanding against the studs, would a little spray foam work to insulate the pipe from the studs?

If it just the pipe expanding, would foam insulating tubes eliminate the sound?

plumberinlaw 03-01-2011 11:24 AM

Try it and let us know.

madamd 02-17-2012 11:54 AM

I have this exact problem! I only hear "leaking" noise when hot water is running!!!

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