We had a leak in our upstairs bathroom, about 2 weeks after we had a new ceiling put up and painted in the room below. It wasn't a major leak, but it caused quite a wide line to show up on the ceiling.
I've painted over the line 3 times now, but it just keeps reappearing, is there anything I can do to stop the water mark from showing up?
Stains will usually come right through a new coat of paint.
Did you prime it first? In my experience I've found that a good oil (or even better, shellac) based primer works best for keeping stains from bleeding through the paint.
Leave it to dry thoroughly. This might take several weeks, I'm afraid.
Once dry, try an exterior-grade primer before two or three more coats of paint.
Use the expensive kilz primer then repaint. The oilbase spraypaint primer is also a good idea but don't over spray.
I have had good luck with the Kilz brand of primer, but I'm sure any quality stain hiding primer would work well.
We had massive leaks through our ceiling during a renovation. The ceiling had to be sealed first. Our painter mixed in 4 litres of sealant with the undercoat (again, massive leaks). Even this did not totally help - some stains still came through.
As the new stains came through, we sprayed them with a can version of the sealant (White King Stain Stop Sealer) then repainted the stains. That seems to have done it.
