Just noticed a brown stain on my dinning room ceiling. It's almost directly above a cast iron radiator on the second floor. I know the water in the system gets iron deposits which must be why it's brown. The heating system was running when I noticed the stain and checked the upstairs radiator. The ceiling and radiator were bone dry. I'm guessing the leak is at the union. Any idea on what the least invasive way to figure this out is?

I would guess I need to take the value off then the pipe connected to the elbow. If I'm lucky the problem will be there, right? If the problem is on the other side of the union, what then? Thank you, greatly.

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1 Answer 1


Water can run for some distance inside a ceiling before finding a path to visibility, so the leak might not be where you think it is. Check all the radiators above the first floor for visible leaks or wetness.

The leak could be very small and intermittent, for example dripping only when the system first comes on and warms up, then drying off before you see it on the pipe. Try this -- wrap all suspect pipes with clean paper towels or similar tissue and periodically check for staining.

Another possibility is that the stain isn't from the heating system at all, but is the result of a bog standard domestic spill near the radiator, and some of the liquid found its way through the pipe hole in the floor before it was cleaned up.

Getting rid of the stain is complicated by the fact that the puddle above the ceiling is larger and wetter than the visible stain. You want to make sure it's completely dry before applying stain remover and paint.

  • I really appreciate the response. I'll check periodically around the other radiators and floor above the stain. I'm just concerned the leak is in the second floors subfloor piping. Maybe this is the sign to switch to a new heating system. Maybe forces hot air. :-(
    – user44111
    Mar 26, 2016 at 21:01

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