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I have a kitchen faucet that allows water to back flow through the pipes. The way that works is that you turn on the main faucet handle to warm water, then turn off the water at the at the faucet and don't use the sprayer. The faucet in question is this one.

When the main faucet handle is on warm, but the faucet is off, it allows the hot and the cold water to mix. I notice this for example when a hose is turned on outside. I hear water flowing through the kitchen faucet. I think that means that the hot water is getting to the hose through the kitchen faucet.

I can prevent it by turning off the main kitchen faucet. I can also prevent it by having the water temperature set to full hot or full cold at the kitchen faucet, even with it turned on. We'd like to be able to leave the water turned on warm at this faucet so that the sprayer is available easily.

I was thinking that the solution could be check valves. Are there check valves I could install myself, like ones that screw onto the supply lines?

How do I solve the hot and cold water mixing problem at this faucet?

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They make in-line "spring-type" check valves. Commonly found in 1/2" pipe thread, you may need to adapt to install on your hot/cold supply lines, but it certainly is possible to do.

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  • Any advice on figuring out what size and threading I need? The valves under the sink do screw onto the pipe, I think with a pressure nut. Is that NPT threading or something else? – Stephen Ostermiller May 29 '17 at 9:35
  • If your sink is connected with 3/8 hose to the wall stops, you should use a simple 3/8 compression check valve. Shut off the valve at the wall, unscrew hose, screw in check valve and reattach the hose. amazon.com/Brass-016419-25-8-Inch-Compression-Assembly/dp/… – pdd May 29 '17 at 17:27
  • Great, those look like exactly what I need. – Stephen Ostermiller May 30 '17 at 10:21
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That does not mean water is flowing through the kitchen mixing valve, merely that the sound of moving water is heard at the kitchen faucet. Turn off the hot cut-off valve for the kitchen faucet. Turn on the outside faucet. I'll bet you still hear the sound of the water, but there cannot be flow from hot to cold or vice versa.

EDIT

Turning the hot cut-off off is only to show that the sound you are hearing is not the sound of flow through the closed kitchen faucet. I'm not suggesting you leave it that way. I think the sound is coming through the cold water pipe.

These single lever faucets can sometimes leak through the cartridge, but it is nearly always a slow peak. If it were doing this, you would just replace the cartridge or use a rebuilt kit with new seals.

EDIT 2

So it really is flowing through the mixing valve! My solution would be to keep the valve in the closed position. This also would prevent the sprayer line from being constantly under pressure.

We don't have that kind of kitchen faucet, but a more basic one and we either use it in full cold or full hot position. With our copper plumbing we can hear the sound of an outside faucet on full through an inside wall and can feel the vibration on the kitchen faucet, even when the faucet valve is off.

Yikes, I had not thought about the possible flow path in your faucet and didn't carefully read your original post! The outside faucets have no flow restriction and if an outside faucet is on the same leg as the kitchen faucet, then turning such an outside faucet on full could lower the pressure on the cold water enough to allow flow from the hot side into the cold side.

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    If I turn off the hot water under the sink, the sound stops. I don't see why it wouldn't flow straight through the cartridge when the cartridge is left full open. – Stephen Ostermiller May 29 '17 at 9:30
  • I think you are right and I was wrong. We don't have that kind of kitchen faucet, but a more basic one and we either use it in full cold or full hot position. Also with our copper plumbing we can hear the sound of an outside faucet on full through a wall and can feel the vibration on the kitchen faucet. I had not thought about the possible flow path in your faucet and didn't carefully read your original post. The outside faucets have no flow restriction so turning one on could lower the pressure on the cold water enough to allow flow from the hot side into the cold side. – Jim Stewart May 29 '17 at 15:41

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