Why does it take time for the sink faucet to get hot, but gets cold right away even when it’s already hot?

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Why does it take time for the sink faucet to get hot, but gets cold right away even when it’s already hot?

In: Engineering
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The water gets cold inside the plumbing over time. It takes some time for the hot water to come again through all the pipes. But the cold water is already cold, and already there.

Faucets don’t magically produce water of different temperatures on their own. They are valves that open and close pipes, the cold directly from the main source of water and the hot from a device that heats water.

The device that heats water (a “water heater”) has hot water within it that is maintained at increased temperature waiting on use. But the pipe leading from it to the faucet is full of unheated water which needs to be pushed out ahead of the hot water. This is why it takes time for the water from the faucet to get hot.

The cold water source is always unheated. Opening it always gives cool water instantly.

There are two water lines going to your sink, one for cold and one for hot. Depending on your sink, you either have two valves, one that controls the hot and one for cold, or you have a single valve which controls how much water from each pipe comes out.

The water heater is a device that does exactly that, it takes your water and heats it up before it is sent to the faucet. The problem is, if you haven’t used the hot water in a while, the water in the pipes between the heater and your faucet will cool down. When you turn on the hot faucet, it starts pumping hot water again, but all the cold water needs to be flushed out before the hot water can reach you. Also, the pipes themselves will absorb some of the heat, so that will add a little time before you get hot water.

In your question “Why does it take time for the sink faucet to get hot, but gets cold right away even when it’s already hot?”, the reason it gets cold right away as you are just switching from the hot pipe to the cold pipe, which is already cold. If you switch back to the hot pipe again, it will be hot immediately. It is when it sits for a while without use is when the water will cool off again.