Here's Why Your Tankless Water Heater Keeps Giving You A Cold Water Sandwich

While a "cold water sandwich" might sound like something you'd order at a sketchy 24-hour diner, it's actually not a sandwich at all — it's an unwelcome surprise during your would-be hot shower. Whether you shower in the morning or evening, you may have encountered a sudden blast of cold water in between warmth if you have a tankless water heater. This uncomfortable wake-up call has been dubbed the "cold water sandwich effect" by plumbers.

The cold water sandwich occurs due to fluctuating water temperatures; this can be caused by back-to-back use of plumbing fixtures, which stresses the tankless water heater. The quick burst of cold doesn't necessarily indicate trouble with your heater, but it can occur because of system errors and overuse of the equipment. There are ways to work around this annoyance, such as letting the shower run before you get in it, but it's still worth checking your tankless water heater for problems. Certain issues can make your water heater less efficient over time, which can increase your energy bills. Since a high energy bill is an even worse shock than a bit of cold water in the morning, you should check your tankless water heater as soon as you notice repeated "sandwiches." Even though the cold water sandwich is not necessarily a cause for alarm, checking the tankless unit ensures you don't miss a sign that you need to replace your water heater.

There are a few reasons why your tankless water heater could be spitting out cold water. The first is the size of your water heater. If you have a large household with a high demand for hot water, consider upgrading to a larger unit to keep up with your home's needs, which include appliances like dishwashers and washing machines. Another cause of the cold water sandwich is a broken flow sensor. The flow sensor is responsible for measuring the amount of water passing through the system and communicating that measurement to the unit's control board. When operating properly, the flow sensor should detect a change in temperature and adjust accordingly, so an unevenness in temperature may be a sign that the sensor is not working correctly.

If you are not properly maintaining your tankless water heater, it may begin to exhibit the cold water sandwich effect. Due to regular use, the system incurs damage over time. A dirty water filter, corroded water lines, and mineral buildup can all cause your tankless water heater to work less effectively, resulting in those dreaded sudden water temperature changes.

In addition to regular maintenance and resizing your tankless water heater to keep up with your household's needs, there are several ways you can rid yourself of that nasty cold water sandwich. If you have an electric tankless water heater, you might want to consider switching to gas. Gas water heaters can change water temperature more quickly than electric water heaters, though they are typically not as efficient and can prove costly.

Rather than replacing your tankless water heater altogether, you can make small additions to improve your heater's performance. By installing a recirculation system, you can ensure that hot water is always circulating through your pipes, which helps it get to your tap faster. Implementing a recirculation system especially benefits those with larger homes where water must travel a greater distance from the heater to appliances. You can also install a buffer tank to support your tankless water heater. This auxiliary tank holds hot water and releases it during transitional periods when the main tank is slow to heat up, filling in to remove the cold water sandwich effect. Water-saving fixtures and optimized heater settings can also decrease the likelihood that you'll experience a cold shock — and they'll also help you conserve water in your home, saving you money in the long run.