Hi - My home was built in 1938 and has a basement, main floor and 2nd floor. A few weeks ago, water was dripping from a main floor door frame below the 2nd floor bathroom. No water was leaking into that bathroom. The supply pipes are galvanized, so pin hole leak unlikely. All supply valves to sink and tub were dry. After turning the upstairs supply off, we turned different combinations of toilet/tub/sink water off to see where it might be coming from. It wouldn't happen again. We turned everything back on, and no leaking for 2 weeks. Then, all of a sudden, it's leaking again. Turned the upstairs supply off and it eventually stopped. Since all upstairs supply valves are dry, and there's no copper pipe, where could the leak be? Also, why was it okay for 2 weeks, then started again? And this was a lot of dripping - not just a slow drip. Probably 8 gallons over 5 hours. Plaster walls and ceilings, of course! Thanks for any help!

"galvanized, so pin hole leak unlikely" no, actually very likely. This could also be a drain issue rather than a supply problem. You will eventually need to tear open the ceiling below the bathroom. That water has done more damage to the structure than you know. Once the ceiling is open your detection job will be easier

Okay, but if it's drain problem, then why would shutting off the supply stop it? I just turned on the hot water supply by itself and the leak started up again. The drips don't feel warm...

Like Bob, I was thinking drainage leak until I came across this,
Turned the upstairs supply off and it eventually stopped. So we have a pressure leak. Follow Bobs advice and open up the ceiling to locate the source. When you have located the leak get back to us for a solution. Good luck, Tom

We are playing blind here so be patient. Did you NOT shut down the supply and find that the drip continues? Shutting off your supply and the drip stops butthat could be because with no supply you no longer have anything draining.

Thank you, Tom and Bob. I have now made the leak start even with the supply cut off to the upstairs bathroom. I have a friend coming tomorrow, and we will probably start on the ceiling. Dang - what a mess this is going to be. I'll keep you posted. Dana

Sorry about the ceiling but it must be replaced anyway. You may not see it but , by now, you have mold inside the cavity

By the way, is the reason for going through the ceiling as opposed to the floor that's it's easier? I'm wondering if I should take this opportunity to remodel, in which case I would put a new floor in...

The ceiling must be replaced, we really don't know much about the flooring just yet. The leak could originate inside a wall cavity and not involve the floor but maybe the subfloor