What type of leak only leaks sometimes?

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soparklion11

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That sounds like a joke, but it is not. I found a small puddle ~4oz of water that had spilled out from the trim where a ceiling meets a wall in my basement. So I opened an 8x8" square. The plumbing for my powder room is directly visible, but the PEX is dry. My 2nd floor full bath is directly above that powder room.

I discovered the water a week ago and everything is still completely dry. I've used both of the sinks, both toilets and the shower since then but the spot in the basement is still dry.

DO I just ignore it and figure that it won't ever happen again?
 

Steve123

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Wrap a paper towel around the suspect joints. Then keep your eye on it.

It can happen that joints only leak sometimes. Doesn't really matter why it only leaks sometimes -- if it leaks it needs to be fixed.
 

JoeD

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The water could have come from the wall or the floor. If there is a wall defect and the shower isn't aimed at it then it won't leak. Perhaps a big spill on the floor came through a crack or air vent.
 

Jeff Handy

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Is there a bath tub?
The overflow drain can leak if the seal against the back side of the tub is going bad.
Or it might only leak during a shower, not a bath, or vice versa.

A heavier person can deflect a loose shower pan or open up caulk joints around an old tub.

And as pointed out, shower leaks can come and go, depending on where the water is shooting at.
Different people showering.
Or a shower curtain not closed up properly.
Washing the dog and splashing water around, which can run under the baseboard.

Maybe a kid ran the sink over, or had a clogged toilet, and did not want to confess their crime?
 

Sparky617

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It could also be a leak from where the plumbing vent exits the roof.

From heavy rain or windblown rain, loose shingles or squirrel or raccoon damage, etc.
I've had this happen twice in two different houses. We were in our last house when Hurricane Fran hit the Raleigh area. I had a wet spot on our family room ceiling which was directly below our master bath shower. After some digging I found that the water was following the vent pipe down because the rubber gasket on the vent was dried and cracked after 15 years or so. Same thing in our current house only this was in our laundry room below our hall shower. The water will generally follow the outside of the pipe and drip when it his a fitting, especially if it turns a corner. It only ever appeared in a really heavy rain. They make a rubber donut you can put on the pipe to reseal it. You don't want to mess around with replacing the boot if you're not ready for a new roof as you can break shingles and cause a bigger problem. There are better boots out that that prevent this, but they aren't the usual ones roofers use.
 

Jeff Handy

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It could also be a clogged gutter, running over and flooding the ground right there.
Or sump pump discharge pipe cracked joint,
Or a furnace exhaust or water heater exhaust leaking, pvc joint failed.

Or a dryer vent cover leaking.

Bath fan vent cover leaking.

Or a window frame leaking.

Dozens more possibilities.
 

Steve123

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It would be nice if leaks got better and fixed themselves over time.

But they don't.

Might take a while, but you will find the source.
 

billshack

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Sometimes i have found leaks like this that were caused by a person getting out of the shower and water landed on the floor which then went through a crack to the room below.
 

EricK

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I once found a tricky leak for a customer. He said the shower leaks sometimes but not always. So I knew it wasn't the p-trap or the drain. The shower had a wand so we sprayed each of the three handles on the wall; hot, cold and diverter. As soon as we hit the diverter water started going down the inside of the wall. Turned out there was a little gap behind the trim letting water through the hole the pipe came out. So you may want to have one person watch from below while another person hits everything with a stream of water.
 

soparklion11

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Thank you all for your ideas. Because I last had a mystery leak when it was raining, I think that the roof vent is the culprit. I wish that I could get onto my roof, but it is slate.

I like the vent because I also had a mystery drip in the ceiling of the powder room (in the same wall, just one floor above) and after a paper towel wrapped around the joints was dry for a year with just a piece of drywall mounted, I finally decided to finish it... one week before this leak was discovered in the basement. When that piece of ceiling was open, the toilet plumbing looked good from below and there isn't water behind it either.

The two bathrooms above the leak don't get a lot of splashing; no kids, no dog, and at 168 lbs I don't stress the tub, which is on the opposite wall from the leak.
 

Jeff Handy

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Wrap an old towel around the vent pipe in the attic.
Secure it with duct tape or some wire, like from a metal hanger.
The old towel will intercept any small drips running down the pipe, and will absorb the water, then slowly release it through evaporation.
 

Guzzle

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For immediate notification, somebody makes a water level detector that looks like a flying saucer and sounds an alarm. Works on a battery, might detect 1/16" inch or so of water, cost $16.
 

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