What is a Cold Water Sandwich?

Even if you don’t know what a “cold water sandwich” is, you’ve likely experienced it. In this article, we’ll cover what causes this common water temperature effect and let you know the various ways in which you can solve it. A cold water sandwich might sound like fun, but it’s more of a nuisance.

A cold water sandwich is an effect that occurs after you turn on your faucet or tap, and the water temperature rapidly shifts back and forth. More specifically, the water is warm when you first turn on your tap then there is a short period of cold water, and then it gets warm again (or whichever temperature you set your faucet to).

Effectively, the cold water is sandwiched by two periods of hot water, hence the name. It’s not usually much of an issue, but it can be quite an annoyance! Below, we’ll dive into more detail about what causes this effect and let you know what you can do to resolve it.

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Understanding Your Tankless Water Heater – What is a Cold Water Sandwich?

Now that you know what the cold water sandwich effect is, let’s explain what causes it. A cold water sandwich is the result of your tankless water heater. Those without a tankless water heater shouldn’t experience this effect. Therefore, to understand the cold water sandwich effect, we must understand how a tankless water heater works.

A tankless water heater heats water as it passes through the unit. While a tanked water heater heats a large amount of water and keeps it in a reservoir, the tankless water heater has a more instantaneous effect. The tankless water heater heats the water, passes it through pipes to your faucet, and you’ve got warm water!

Now, how does this relate to the cold water sandwich? The cold water sandwich occurs when you have recently used your tap for hot water. The next time you turn on your faucet, you’ll experience a short burst of hot water, which is the water heated from the last time you used it, but that is still sitting in your pipes, between the water heater and the faucet.

Once this water is used, you’ll get a short burst of cold water, which is the water that is servicing your home from outside. This water hasn’t had the chance to be heated because the water heater has not come up to temperature. Then, once the tank comes up to temperature, you get another burst of warm water, thus completing the cold water sandwich!

As you can see, it’s a perfectly normal process and something that most people who use a tankless water heater will experience. It’s especially prevalent in the colder months because the water in your pipes will be colder and will take longer to heat with your tankless water heater.

Either way, it’s nothing to be concerned about, and it’s little more than an annoyance. That said, you can still choose to address this annoyance, and we’ll cover that next.

How Do I Stop the Cold Water Sandwich Effect?

There’s no shame in wanting everything in your house to work perfectly. So if you’re very intent on fixing your cold water sandwich effect, then more power to you. Unfortunately, there’s not usually a quick fix for this problem. Here are the ways that you can address this issue:

Recirculating Pump

This is generally considered the easiest solution and might also be the most practical. A recirculating pump is a device that can be attached to your tankless water heater (and is even included with certain models).

A recirculating pump addresses the problem that occurs when the water between your water heater and faucet becomes cold between uses.

A recirculating pump attaches near the faucet and recirculates the hot water back to the pump between uses. A thermometer detects if the water has gone cold and sends it back to the water heater. The obvious downside here is the extra expense to heat your water!

Additionally, a recirculating pump doesn’t technically solve the cold water sandwich problem, but it does give you more reliable access to hot water.


Perhaps the most effective method is, well, to get a better water heater! We know it’s an obvious piece of advice, but it’s also usually the most effective. A cold water sandwich may signal that your tankless water heater is getting old and can’t get up to temp with the speed and efficiency it once could. It’s reason enough to upgrade.

Many users choose to upgrade to a gas tankless heater because they can get up to temp quicker. Additionally, many newer models will keep the water heater running for a short period after use, which prevents the cold water sandwich effect during frequent water usage.

Storage Tank

Our final solution is to install a mini water storage tank next to your tankless water heater. Essentially, this combines the benefits of tanked and tankless water heaters. The small tank is attached to the tankless heater, and water flows through the tank before use.

The tank holds a decent amount of warm water, which should hold you over long enough for the tankless heater to heat up, thus canceling the cold water sandwich effect.

As a bonus, it won’t use as much power as a recirculating pump, and it won’t be as difficult to install. That said, space might be an issue with installation, and you may not have any room for this tank.


Thanks for reading our in-depth guide to the cold water sandwich! While it’s not usually a pressing issue, it could be a sign of an aging water heater that should be replaced. Use our guide above to decide on the best solution for you!

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