You say the plaster is peeling, but that hole looks like it has an over-driven sheetrock screw in it. Is it really drywall? And is it possible someone drove a screw into a plumbing pipe?

i think it's termites. :( :( I can't imagine that someone drove a screw in there. It's just the painters painting. And i think it just appeared out of nowhere. Painter seemed perplexed.

oh, really ??!! I was imagining it to be a termites head or mud tube or whatever.

Oh!!!! now it looks obvious to me it's a Phillips head screw! Still a problem, but not the big problem I thought it was! Hmmm....now how to deal with that?! Would painters use screws?

No, painters wouldn’t put in screws. It looks like the joint compound fell out of the hole, but I don’t know why that would happen and take paint with it unless there is moisture there, which is why I asked about someone driving a screw into a plastic pipe in the ceiling....

oh! Well, it's definitely discolored as if there's moisture. And the area of discoloration has gotten bigger! So i turned off the main water shut off valve and drained the pipes until we can have a plumber take a look. Thank you so much for the diagnosis!!

I’m not sure that’s the correct diagnosis, but it is odd to have that happening. If there is moisture there, it could also be coming from a leaky wax seal on a toilet, or from a leaky shower enclosure, etc. Is there a bathroom anywhere in the vicinity above that spot?

no bathroom. It's just a bedroom floor

Ok. Since you say the discoloration is getting larger, I’d gently probe in and around the hole with a small screwdriver to see if there is any soft, moisture-containing material around the screw head.

and if there is? I turned off water last night, and will check this morning to see if discoloration got bigger (or smaller) since I turned off the water.

Had someone take a look, and it's probably from a leaky roof section on the roof above (it sticks out from the top floor. Or the window above. Let's hope it was just that roof that he caulked.

If there’s moisture, it’s some kind of leak to address. If there’s no moisture, it’s something else, and maybe not so worrisome. But the fact that the spot is getting larger is troublesome.

Where is that hole in the ceiling? Like, is it close to a wall, or is it out in the middle of a joist span?

How close to the middle?

the wall above is further in than the wall in that room, and the hole us just under the wall above (We forgot that the wall above is further in). I know i'm not using the right vocabulary to describe!

From what I can understand from your description, that could indicate some kind of roofing/flashing leak.

Okay, so the hole being under a wall above probably means that although the above wall is not "load bearing" it is enough weight that where your hole is, is likely the low point in the deflection of the joist span for the floor above. This means water could be coming from any number of places in your walls: plumbing, roof leak, siding leak, virtually anywhere, and if it is inside your walls remember the rule: water runs down hill ALWAYS. So if it is coming from plumbing, or the roof or wherever it is seeking this low point in your ceiling and then seeping through. It's probably a very slow leak, but until you find it that hole isn't going away.

The person who looked at it found the flashing needed repair and also found a torn shingle. He repaired those items and said it could also be the window (because it was rotted). So we opted to repair roof/flashing and see if leaking continues. If it does, we'll have to replace that window sooner rather than later! Does that sound reasonable to you guys? There's no bathroom above, so pipes would be less likely, right?

Since that plug fell out to reveal this, and you just bought the house, it sounds a bit like previous owners did a cover up fix, and probably knew about this problem.

Torn or missing shingle or bad flashing could absolutely cause water to turn up in odd places. When we had a missing shingle, we had water dripping from a first floor doorframe during a hard rain ... it stopped raining in the house when the shingle was replaced. We also had an issue when a roofer messed up some of the flashing (separate situation, totally different section of the house) which also had water dripping down the beams. Got a new roofer and new flash, and there was no more water.

Rotten window is something you probably don't want to wait too long to fix, whether it's the culprit or not, rot is not something you want to leave in place.

Pipes could be anywhere, depending on how they were run. However, someone driving a sheetrock screw into a pipe near the edge of a stud/joist would only cause damage if the water pipe was plastic, not galvanized.

Also, although water does seek the lowest point, it can do so by traveling sideways. I once had a ceiling leak that was located 10' away -- laterally -- from where the water was getting in.

Thanks, everyone!! No more discoloration or issues in that area after roof repair, in case anyone was interested in the outcome. Thank you!!!