When water stops flowing from the spout of your kitchen faucet, it might mean that something inside the faucet is blocking it. If you want the faucet to work properly, you have to find the blockage. It's in one of three places: the aerator, the spray diverter or the faucet valve. The aerator is the easiest to check because it doesn't involve disassembly of the faucet. If the sprayer works but the faucet doesn't, the spray diverter is the most likely culprit.
Inspect and Clean the Aerator
The aerator is the screen fitting on the tip of the faucet spout, and you can often unscrew it with your fingers or with pliers. Not all aerators fit on the outside of the spout, though. Some have male threads and are recessed inside the spout.
The procedure for removing one of these cache aerators can seem mysterious, but it really isn't. Try using your finger, and if that doesn't work, you need an aerator key. If you don't have the one that came with the faucet, you can buy one at any hardware store for less than $5. Fit the key into the notches of the aerator and turn it counterclockwise to remove the aerator.
Once the aerator is out, try the faucet. If the flow from the spout is normal, soak the aerator overnight in vinegar to clean it. If you still get nothing from the spout, you can go ahead and back flush the aerator under the sprayer and replace it, but now you have to disassemble the faucet.
Check the Sink Faucet Diverter Valve
The spray diverter works exactly like the one on your tub spout that shuts off water to the spout and sends it to the shower when you engage it. Faucet diverter valves take all kinds of shapes, so check the manufacturer's website for the exact shape and location of yours. In all likelihood, it's a small plastic valve inserted in the valve at the base of the spout, and you have to remove the spout to access it.
This operation is usually fairly simple, and you may not need to shut off the water. On many models, such as Kohler single-handle faucets, you can unscrew and remove the faucet handle, then wiggle the spout back and forth while you apply upward pressure, and the spout should pop off. The diverter, which is smaller than a dime, is inserted in the valve housing. You can pull it out with needle-nose pliers and replace it.
On other models, the diverter is under the valve cartridge. You have to pull out the cartridge to access it, which requires shutting off the water. On widespread faucets, the diverter is in a tee fitting joining the hoses that connect the handles to the spout and sprayer, and you access it by disconnecting the hoses from the tee with a wrench. If the diverter is the culprit, you'll resolve the faucet issue by soaking it overnight in vinegar or replacing it.
Clean/Replace the Faucet Valve
Still getting no flow from the spout? Since you've eliminated the diverter and aerator as reasons why water is only coming out of the sprayer, the blockage must be in the valve, which is fairly common with cartridge valves. The cartridge is easy to clean; just pull it out and soak it overnight in vinegar. Usually when a cartridge gets clogged enough to stop flow, though, it's better to replace it. It has to be fairly old to get this clogged, so it's probably overdue for replacement anyway.
Chris Deziel is a contractor, builder and general fix-it pro who has been active in the construction trades for 40 years. He has degrees in science and humanities and years of teaching experience. An avid craftsman and musician, Deziel began writing on home improvement topics in 2010. He worked as an expert consultant with eHow Now and Pro Referral -- a Home Depot site. A DIYer by nature, Deziel regularly shares tips and tricks for a better home and garden at Hunker.com.