Troubleshooting Tankless Water Heaters and How to Solve Problems

Tankless water heaters can be a wonderful upgrade for virtually any home. Common in Europe and Japan, homeowners in the U.S. are benefitting from the increased popularity of this technology today. When installed properly, virtually endless hot water is possible when these water heaters are used within their capabilities.

Even the best tankless water heaters can encounter issues or problems that may cause the unit to not work properly. If you’re encountering a problem with your new tankless system, here are some of the common concerns that owners encounter and how you can solve them.

How Come I Don’t Have Hot Water Right Away?

To provide immediate hot water to a tap, a tankless hot water system must be equipped with a recirculation solution. This comes at an added cost and may not be available with all systems. For systems without a recirculation system, hot water can be provided in just seconds, depending on the distance of the tap from the tankless water heater.

Can I Receive Hot Water if I Lose Power?

Tankless hot water systems which operate on electrical power will not function if there is a loss of power at the home. Some gas-powered systems may continue to operate, depending upon how fuel is supplied to the unit. If you’re concerned about losing hot water with a power outage, many tankless systems are equipped to work with battery-based power storage in emergency situations.

Can I Use a Tankless Water Heater with a Low-Flow System?

Most tankless water heaters are compatible with low-flow shower heads, faucets, and aerators. If you find that the water temperature with your low-flow components is not hot enough, some systems can benefit from a thermostat reduction. Although the temperature is technically lower, the mixture of hot water and cold water works in a way that benefits a low-flow system.

Some faucets are equipped with limit stops that can affect your water temperature mixture as well. In some situations, these stops may need to be removed to resolve concerns in this area.

What Are the Maintenance Requirements for My Tankless System?

Tankless water heaters tend to require two types of ongoing service to continue operating at peak efficiency levels. Many come equipped with a filter that removes debris from the incoming water supply. This filter may need to be checked monthly, if not earlier, to ensure no blockages are present that would alter water-flow dynamics.

Tankless water heaters must be flushed periodically as well. This maintenance issue is dependent upon the hardness of the water at the home. Most flushing requirements are listed as a 1- to 5-year maintenance need by system manufacturers.

For more tips on tankless water heater maintenance check out our post here.

Why Does the Fan on My Water Heater Keep Running?

The fan on a tankless system continues to operate after hot water use is terminated to ensure there is an available supply the next time. This eliminates temperature fluctuations that can occur when water is started and stopped throughout the day. The fan operation will continue for gas-powered units to ensure the flue has been cleared of any exhaust elements as well.

What Size of Gas Line is Required for a Tankless Water Heater?

Most tankless water heaters operate off a 1/2-inch or 3/4-inch gas line. Which is required will depend on what can provide a sufficient level of fuel to the water heater.

Undersized gas lines can place stress on the water heater, reduce its expected lifespan, and even be a warranty violation for some manufacturers. For this reason, installing a new gas line is usually reserved for professional technicians.

What Gas Can I Use for My Tankless Water Heater?

Most tankless water heaters operate off of natural gas or propane. Some manufacturers, such as Rinnai, offer field conversion kits that can transform a natural gas water heater to accept propane, or the reverse. These kits are usually reserved for tankless systems that have already been installed and the home experiences a fuel availability change outside of their control.

Where Can I Purchase an Uninterrupted Power Supply for my water heater?

Most tankless system manufacturers do not offer a battery backup power supply to keep the unit operational during a power outage. Some may offer recommendations on third-party products or provide exact specifications that an uninterrupted power supply must meet. Be sure to follow these instructions to the letter and contact the customer service line of the manufacturer with any questions you may have.

A tankless hot water system can be a wonderful upgrade for almost every home. With these troubleshooting tips, you’ll be able to work on resolving issues when they come up, allowing you to have the hot water you need, when you need it. Check out our top-rated tankless water heaters here.

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  1. Tom linder

    December 11, 2019 at 3:11 am

    Tankless water heater doing poorly keeping up during showers. Sometimes it gets a power fail. Operating temp is 135 and the unit has been flushed. Could it be a bad thermerl rod or what meters the temp.


    • Gregory

      May 11, 2020 at 5:10 am

      We’d recommend having it checked out by a licensed plumber.


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Greg Mattson

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