How to Back-Flush a Kitchen Faucet

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Low flow from a kitchen tap could mean that sediment has collected in the faucet or pipes and is blocking the water. You can usually clear the sediment by backflushing the faucet and the supply pipes, but before you do that, you should try a few other remedies first. It isn't that difficult to backflush the pipes, but the other remedies are even easier, and they solve more common causes for the problem.

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The problem is fairly easy to handle if only the kitchen faucet is affected because you can narrow your activity to the faucet itself and the pipes that service it. The most common cause for low flow is a blocked aerator, followed by sediment in the faucet valve and finally debris in the supply lines. It's best to start with the aerator.

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How to Check and Clean the Aerator

The aerator is the screen-like attachment on the end of the faucet spout. When hard water deposits and rust collect in the screen, they effectively reduce flow from the faucet. Here's how to check it and clean it, if necessary:

  1. Turn the faucet off and unscrew the aerator. You may be able to do this by hand, but if not, use a pair of locking pliers. It's a good idea to wrap the aerator with a rag before gripping it with pliers to prevent damage to the finish.
  2. Turn on the faucet, and if the flow has returned to normal, the aerator needs to be cleaned. If the flow is still low, the aerator isn't at fault, so you can replace it.
  3. Clean the aerator by soaking it overnight in vinegar, which will dissolve the scale and rust blocking the screen. Replace it in the morning.

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When you remove the aerator, check the screen for damage and replace it if necessary. You can find replacement screens at any hardware store, but if not, replace the entire aerator. A new one costs less than $5.

If you have a pull-down kitchen faucet, there's no aerator, but the spout can still get blocked. Even though you usually can't unscrew and remove the spout, there's an easy way to check if it's blocked. Pull it out, clamp the hose so it won't retract and soak the spout overnight in vinegar. If it works normally in the morning, it was blocked, and now it isn't.

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How to Flush the Faucet and Clean the Valves

Scale and rust can also collect inside the faucet body and in the valves. To clear it, you need to turn off the shutoff valves under the sink, disassemble the faucet and remove the faucet valve or valves. You need a hex wrench or Phillips-head screwdriver to remove a faucet handle. After that, you can use your pliers to unscrew the retaining nut or pull the retaining pin and pull out the valve.

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Once you've done this, it's easy to flush a kitchen faucet, but it can get messy, so have a bucket and some rags handy. Open the cold water shutoff valve gradually and allow water to stream out from the valve opening, using the bucket to catch water that shoots out beyond the sink. Let the water flow for about 30 seconds, then close the cold water shutoff, open the hot one and repeat the procedure.

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Flushing the faucet will get rid of any sediment inside the valve housing, but the valve (or valves) may have small holes that can also get blocked. Soak them overnight in vinegar to dissolve scale or rust that prevents water from flowing. Vinegar is hard on rubber, so remove any O-rings or rubber gaskets before soaking the valve.

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How to Backflush the Supply Hoses and the Shutoff Valves

If you still notice low flow after flushing the faucet, the next step is to backflush the supply hoses. The purpose of this procedure is to get rid of sediment blocking the pipes that supply the shutoff valves.

  1. Turn off the valve on the hot water heater and open the hot side of the kitchen faucet to make sure there's no pressure.
  2. Plug the aerator on the faucet with a dime or similar object. If you have a pull-down kitchen faucet, toggle the lever on the spout to turn the water output off.
  3. Find a faucet in the house with a large spout unlikely to get blocked by debris. Preferably, it's as close to the water heater as possible; the faucet in the laundry utility sink is usually ideal. Open the hot water side of the faucet and cover the drain so you can see what comes out of the faucet.
  4. Go back to the kitchen faucet, turn on the cold side all the way and listen for water flow. Leave the water on for a minute or two, then turn it off.
  5. Close the hot side of the secondary faucet, then try the kitchen faucet to see if the flow has improved.

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You can use this procedure to backflush the cold side, but you'll have to turn off the water to the entire house and use an external supply, such as a hose connected to a neighbor's outdoor faucet and connected to the kitchen faucet spout with an adapter. This is more troublesome, but fortunately, you probably won't have to do it because flushing the hot side gets rid of most blockages.

Backflushing Didn't Work — Now What?

If you live in an older house with galvanized steel pipes and you can't restore pressure by backflushing, it's probably because the pipes are corroded. Corrosion is one of the main drawbacks of galvanized plumbing and one of the reasons it isn't used anymore for indoor plumbing.

Corrosion is basically rust. As it grows inside the pipe, it gradually restricts water flow while at the same time weakening the pipe joints and eventually causing leaks. If the pipes are corroded, you'll see a lot of rust coming out of the secondary faucet when you use the technique for backflushing the valves and supply pipes.

Unfortunately, there's no quick and easy way to deal with corroded galvanized pipes. Once you realize the pipes are corroded, it's time to think about replacing them with copper or PEX pipes, which are more sanitary and won't corrode. Your best bet at this point is to call a plumber so you can discuss your options.