I bet somewhere in the faucet the installer used a black iron nipple for the spout or shower head. The nipple rust very quickly. A few seconds of water rinses it out. The nipple will start leaking in the future.
It's likely a rusted steel feed pipe and you don't use it often enough to keep the rust buildup flushed out.
If galvanized piping was uset to plum the house, it may have rusted shut, an easy fix would be to run a new line in copper or PEX from the water heater to the valve
rusted root
Rusted Rail was created in 2006.
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The past tense of "rust" is "rusted."
Rusted Angel was created on -19-09-08.
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Rusty hammer to the rusted calipers should do the trick