If you experience a sudden and persistent drop in your kitchen faucet's hot water pressure, you'll need to do a little detective work to pinpoint the origin of the problem. After ruling out a few common culprits, the next cause to consider is a buildup of mineral deposits somewhere within the hot water pipe or faucet. Clearing the pipe can help you adjust the hot water volume on a kitchen faucet.
Adjust Hot Water Volume
First, take inventory of the other appliances in your home that may be running hot water. When your washing machine, dishwasher or shower competes with the kitchen faucet for hot water, you may experience a completely normal and temporary drop in water volume.
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Next, check whether the hot water valve is open all the way at the supply pipe. If you've recently had any repairs done to the faucet or sink, the supply lines may have been closed as a precaution. You'll have poor water pressure coming from the hot water side if that valve is only partially open. Under the sink, locate the hot water valve on the left-hand supply pipe and turn it counterclockwise to open it further.
If the valve is already as open as possible and the hot water pressure is still inadequate, check for any leaks under the sink or around the faucet. Water escaping from the hot water pipe before it can exit the spray head will inevitably decrease the overall volume or pressure of the hot water output. Leaking faucet handles indicate a worn-out cartridge, and leaking supply pipe connections also warrant replacement.
Sediment Buildup in Faucets
When none of the easy fixes seem appropriate, you probably have a clog somewhere in the faucet or the supply pipe. Yes, even potable water pipes can get clogged, although it usually occurs very gradually.
So-called "hard water" has a high concentration of minerals dissolved within it, but when the water passes through the pipe or evaporates from a surface, these minerals get left behind. Over time, one microscopic mineral crystal turns into a glob of minerals that blocks the pipe.
Find Mineral Deposits in Faucet
To find and flush these mineral deposits, first try to pinpoint where the buildup is located. Chuck Barron details how to locate buildup that restricts hot water flow in his YouTube video. Unscrew the spray head from the faucet and turn on the hot water. If the water volume increased, then the clog is in the spray head. Use the aerator key that came with your faucet to remove the aerator and access the check valve in order to thoroughly inspect and rinse these pieces.
Next, go under the sink and completely close the hot water valve. Disconnect the flexible line connecting the hot water pipe up to the faucet. Place the free end of this line inside a bucket to catch the water and open the hot water valve all the way. If the pressure shows improvement, then the sediment is within the faucet itself and the faucet should be replaced.
Finally, disconnect the flexible hot water line directly from the hot water pipe at the valve. Place your bucket under the valve and open it one more time to observe the hot water pressure. If the pressure seems normal at this point, then the clog is in the flexible hot water line and this part should be replaced.
Back Flush the Lines
Aside from replacing the parts clogged with debris, you can attempt to clear the sediment using a technique known as back flushing. With the hot water line disconnected and resting inside a bucket, open the hot water tap and turn on the cold water. Press your hand against the spray head to block the flow of water, forcing it back through the open hot water tap.
With a little bit of luck, this new direction of pressure will force the debris down through the hot water supply line and into your bucket.
If you frequently encounter this problem, consider replacing copper water pipes with plastic versions, which, according to Roto-Rooter, resist mineral buildup altogether.