If water comes out, it means your culprit is a clogged aerator. Clean it with vinegar and a toothbrush. If the aerator isn t the problem, remove the valve stems to see if the gaskets inside are preventing the free flow of water. If your investigation of the faucet proves fruitless, and nothing looks clogged, it s time to scrutinize the nipples that come out of the wall. The nipples and the shut-off valves are usually made of different materials.
Electrolysis occurs when dissimilar metals are in contact.
The resultant corrosion can completely clog the inside of a nipple. We have no idea why the valve always seems to skate through unscathed. The fittings and pipes in the wall could possibly be corroded, as well. This means that the project could turn out to be a big job. Be prepared for this possibility.