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Question DetailsAsked on 2/4/2015

I hear dripping in wall when faucet is turned on but no visable signs of water damage. Is there a leak?

2008 construction, 2story townhome with kitchen, living & master br on second floor. Kitchen and master bath back up to each other with water heater in attic directly above... that’s where leak sounds like it’s coming from. No visible signs of water damage to walls, wood floors in kitchen (2nd story), or 1st floor celling. Leak sounds when master bathroom faucets/shower and kitchen sink are turned on. Starts of fast like a machine gun, slows after 5-10 seconds, then "drips" for about 5 minutes after. Is there actually a leak or is there some other explanation?

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2 Answers


You have identified one of the tougher things to track down.

Things it can be in no particular order though I am thinking #3 is likely your case - plus more I am not thinking of this late at night:

1) leak in basin, tub, toilet that keeps a small amount of water running down the drain pipe, eventually shutting itself off several minutes after the faucet is turned off as the washer molds itself to the seat. If no dripping faucets, not the cause - and since you say occurs after use at several different locations, not likely your cause.

2) a flat section of drain pipe leading into a piece where the vertical is inclined "towards" rather than "away" from the horizontal run coming into it. Explanation - if the pipe is installed so the 90 degree bend downward is actually, including all pipe and joint alignment, slighly more than 90 degrees, small amounts of water running around the 90 continues down the vertical run along the pipe without breaking free of the pipe - so no noticeable noise. However (ditto for gutter downspouts), if the total angle is more than just a little bit less than 90 degrees, then water going around the 90 can drip free down into the vertical pipe, causing a drip or splash when it hits the bottom of the vertical run. Since you have back-to-back use points could be that, but less likely - and usually stops after a minute or so, not 5 minutes,

3) thermal creep - especially with plastic drain pipe and copper water pipes. When the pipes change temperature as the water flows through them (more so with hot water pipe and sewer/drain pipe, obviously), they change length - causing creaking or snapping and popping there they are tight in holes through joists and studs - or sometimes even where just laying on wood or drywall. This could be your case since everything is backed up against each other - could be drain pipe, or the vent pipe leading up to the roof rubbing against wood or firestop where it goes through the floors. Commonly starts up fairly quick - like a machine gun, as you say - and then start tapering off, sometimes taking 3-10 minutes to taper off, with longer and longer intervals between noises. Generally, but not always, can be replicated, and almost always with warm or hot water and strongest with hot-only water if in drain rather than feed pipe. Solution is usually putting plastic isolation sleeves (made for this) or several layers of taped (outside the hole) visqueen around the pipe where it passes through holes in other materials.

4) condensation of flue gas moisture in the water heater flue - either within the water heater itself (flue goes up through the center), or in the exhaust ducting leading away from the water heater, running back down the pipe to the heater. Can hit the burner and sizzle, or miss the burner and land on the flat metal bottom of the heater, causing a tink or splash sound, depending on how much water is accumulating there versus evaporating away again. Generally, unless exhaust duct is quite cold, occurs only at startup until the ducting is to full heat, unless the water heater is actually leaking internally. Obviously, would only occur after hot water use and more than just a bit, and starts up typically maybe 15-60 seconds after water heater fires up.

5) An actual leak, but like you say you do not see wetness - and unless in a drain pipe would generally flow continually if from a water supply pipe. Since occurs after use at several ldraw points, highly unlikely to be from water supply pipes, though could be from a common drain pipe - but would not typically sound above top floor.

6) One other possibility, especially if you are having unusually cold weather (well elow freezing), is thawing of frost in the sewer vent pipe that goes up through the roof - would thaw maybe on sunny warmer days, but could that frost in the attic and above-roof section when you run hot water, which would put warm air up the vent pipe. Listen at pipe, preferably in attic, for this.


I would check the water heater first to see if water is dripping down inside it - either from a leak (unlikely if it dies away) or from condensation upon startup. If this is the case, would only occur when enough hot water is used to kick the water heater into reheat mode.

Try running hot water, then after a bit of a wait cold water only, and see if only does it with one or the other. Usually hot water causes it, because the temperature change in the pipe is much more (about 70 t0 120 or 130 degrees, versus about 70 to 45-55 with cold water.

Try running water into a bucket or pan (so it does not go down drain) and see if makes noise - if so, then creaking water pipe. Try pouring a bucket or two of water down the drain from another source (not from these back to back rooms) - if that causes it, creaking (or leaking) drain pipe.

If unable to track down, get a $10-15 METAL stethoscope at a box store pharmacy area and listen to different pipes to track down the sound. Creaking pipe can commonly sound like a hammering, tapping, clicking, dragging sound, or almost like a drip - sort of like a dull flick of the fingernail against wood. Drip, if falling free so you can hear it, commonly has a bit of a softer/wetter sound more like a swoosh or plink or splash, though I have been fooled both ways. A leak will generally also sound like flowing water or a hiss or whistle in the pipe itself, in addition to any splash or drip sound at the leak point. Listen at walls or pipes with stethoscope and turn a faucet on just a drip to hear what a small leak sounds like. Note - as a beginner you need to turn off all water flow and gas appliances and any type of motor to hear well - and don't let s ticking clock trick you into thinking you have a leak. I have been caught on that one, tracking a non-existent leak. Also, if you leave natural gas appliances (especially furnace and water heater which kick on by themselves) on, you will hear both the main gas flow (fairly clearly) and a small hiss from pilot lights, if you have standing pilots.

From your description, unless it is condensation in the water heater (which is not a major issue unless causing heavy rusting, especially if piling up on and obstructing burner/pilot), I would be guessing plastic drain pipe thermal movement is your cause.

Answered 3 years ago by LCD


Were you able to figure out what the problem was? I have the same issue.

Answered 2 years ago by satoyk

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