How To Winterize A Tankless Water Heater And Protect The Plumbing System

Did you know that even if your tankless water heater is installed inside your home, it can still be susceptible to freezing during cold weather?

Whether you’re planning not to use your tankless water heater for a while or the forecast predicts freezing temperatures, it is crucial to take proactive steps to protect your unit and plumbing system.

Freezing can cause significant damage, leading to costly repairs and inconveniences.

Frozen pipes and winterizing a tankless water heater
photo: pixabay

In this article, we will explore the importance of winterizing your tankless water heater and provide you with essential tips to protect it from freezing during cold weather.

By implementing these preventive measures, you can ensure the longevity and reliability of your tankless water heater, even when not in use, and prevent any potential plumbing issues that may arise.

How To Winterize A Tankless Water Heater: Tips To Get Ready For Cold Winter Weather

To prevent the failure of your unit, follow this step-by-step guide to learn how to winterize a tankless water heater properly.

Many modern tankless water heaters from manufacturers like Rheem, AO Smith, Rinnai, Noritz, Takagi, Bosch, Paloma, and others, incorporate advanced technology and freeze protection features, capable of safeguarding the system from freezing temperatures, even as low as -30°F or lower.

Note: The most effective way to prevent freezing during winter is by installing a tankless water heater in a heated room with wind-resistant features.

However, as the owner of a new tankless water heater, it is important not to solely rely on these features.


Because despite the presence of freeze protection features, all tankless water heaters rely on electric power, including the protection system (usually a heating element or sensor). In the event of a power outage, your tankless unit will fail. This was experienced by many people during the “arctic” winter at the end of 2017.

This is why it is crucial to properly winterize your tankless water heater and be prepared for cold days.

Note: Nearly every tankless heater manufacturer specifies that the unit should not be installed in areas where the temperature can reach 36°F or lower. Failure to take proper precautions, such as correct draining, may result in damages to the tankless unit and its components that will not be covered under warranty. Additionally, adding anti-freeze solution is not recommended as it can cause damage to the heater’s components.

This is especially important if the tankless water heater is installed in locations such as cabins, garages, or if you will be absent for an extended period.

Can Tankless Water Heaters Freeze?

Yes, tankless water heaters can still freeze, albeit to a lesser extent, if certain precautions are not followed. The reason behind this lies in the fact that many modern tankless models come equipped with freeze protection systems, such as electric heaters.

These electric heaters are installed on the heat exchangers and other internal components, activating when the temperature drops below a specific threshold. This mechanism prevents freezing and potential damage to the unit.

In addition, some tankless models are designed to activate the system and heat a small amount of water periodically, effectively keeping it frost-free.

It is important to note that both of these systems rely on a consistent and uninterrupted power supply. Without power, the freeze protection features will be disabled.

Certain manufacturers also recommend the installation of a flue damper to minimize the entry of cold freezing air through the venting system, and insulating the exposed pipes is also advised.

Most models from reputable brands like Rheem, Takagi, Noritz, Rinnai, and others incorporate systems that protect the unit from freezing. Indoor models typically offer protection up to -22°F (assuming no direct wind exposure, also known as the wind-chill effect), while outdoor models provide protection up to -5°F.

Winterizing A Tankless Water Heater: Step-By-Step Guide

Rinnai tankless water heater

One of the key steps in winterizing a tankless water heater is to drain and unplug the unit. By completely removing all water from the pipes, especially the heat exchanger, you can prevent any standing water inside the unit from freezing, expanding, and potentially causing damage.

So, how do you prepare a tankless water heater for winter?

  • Turn the power off. Begin by turning off the electrical power and gas supply. Shut off the gas supply by using the main valve on the gas supply line. For electricity, either unplug the power supply cord or switch off the power at the breaker panel. If the unit has a display on the front, it should be black with no lights.
  • Wait until water cools down. It is important to note that there may still be some hot water inside the unit. If the unit was recently in operation before draining, wait for the hot water to cool down before proceeding.
  • Turn off water. Shut off the water supply to the tankless water heater by closing the main shut-off valve. This ensures that no additional water enters the system during the winterization process.
  • Drain the system. Open all the hot water taps in your home to allow the system to drain and release any remaining water and pressure from the plumbing system. This step is crucial to prevent water from freezing and causing damage.
  • Disconnect the pipes. Carefully disconnect the incoming and outgoing water pipes from the tankless water heater. This ensures that there are no water connections to the unit during the winter months.
  • Remove the inlet water filter. Locate the inlet water filter on your tankless water heater and remove it. This allows for proper draining and prevents any debris from accumulating inside the unit.
  • Ensure all water from the unit is removed. To ensure that all water is removed from the tankless water heater, use a bucket or container to collect any residual water. During the draining process, make sure that the system fully empties, leaving no water behind.

Some manufacturers recommend using air compressors to blow short bursts of air through the inlet connection to ensure that no water remains inside the heater.

By following these steps, your tankless water heater will be free of water and fully winterized.

Can I Fix A Frozen Tankless Water Heater (Unfreeze)?

If your tankless water heater becomes frozen, it is crucial to address the issue promptly and take steps to unfreeze it. The accumulation of ice can cause damage to internal components, particularly those made of plastic, as well as sensors and electronics.

Here are the steps to thaw out your tankless water heater:

  1. Start by checking if your tankless unit or pipes are frozen. Look for any signs of frost or ice accumulation on the unit itself or along the pipes.
  2. If you find that a pipe is frozen, you can use a hair dryer to defrost it. Apply gentle heat along the length of the frozen section, moving the hair dryer back and forth until the ice melts and the pipe is clear.
  3. Before proceeding further, close the gas and water supply to the tankless water heater. This will prevent any potential leaks or water flow while you work on thawing out the unit.
  4. Turn off the power to the tankless water heater by flipping the breaker to the off position. This ensures your safety and prevents any electrical mishaps during the process.
  5. Next, carefully disconnect the unit from its installation and move it to a warmer room if possible. Alternatively, you can apply gentle heat using the hair dryer to warm up the surrounding area of the tankless water heater. It’s important to avoid applying excessive heat directly to sensitive elements like the heat exchanger, as it can cause damage.
  6. Open a hot water tap connected to the tankless water heater. This will allow the flow of water through the system and aid in the thawing process.
  7. Patience is key at this stage. Wait until the entire system thaws completely, ensuring that all ice has melted and water can flow freely.
  8. While the system thaws, carefully inspect the tankless water heater for any signs of leaks or damages. Look for any cracks, broken components, or other visible issues that may require repair or replacement.
  9. Once the system is completely thawed and inspected, drain all the water from the tankless water heater. This helps remove any residual water that may have accumulated during the freezing process.
  10. If everything appears to be in order with the unit and no major damages or leaks are found, reinstall the tankless water heater in its original position.
  11. Open the gas and water valves to restore the supply to the tankless water heater.
  12. Finally, turn the power back on by flipping the breaker to the on position. Ensure that the unit powers up correctly and operates normally.

By following these detailed steps, you can effectively thaw out a frozen tankless water heater and address any potential issues caused by freezing. Remember to prioritize safety and seek professional assistance if you are uncertain or uncomfortable with performing these steps yourself.


While many tankless water heater manufacturers offer models with built-in protection against freezing, it is still advisable to winterize the unit, especially when away from home or during extended periods of inactivity. Unlike tank-type models, tankless water heaters require more attention and extra care due to their delicate features.

Understanding how to winterize a tankless water heater is crucial for preventing freezing and potential damage.

By following the appropriate steps to drain and protect the unit from cold weather, you can ensure its longevity and reliability.

However, if your tankless water heater does become frozen, it is essential to address the issue promptly and take the necessary steps to unfreeze and repair it.

By taking a proactive approach to winterization and addressing freezing issues, you can maintain optimal performance and enjoy uninterrupted hot water supply throughout the colder months.


Why Is There No Hot Water From A Tankless Water Heater During Freezing Weather?

During freezing temperatures, a tankless water heater may not produce hot water due to its built-in freeze protection feature or blocked/frozen pipes. The freeze protection feature is designed to prevent damage to the unit by shutting off water flow when freezing conditions are detected. Blocked or frozen pipes can also restrict water flow, resulting in a lack of hot water. Once the freezing conditions subside or the pipes thaw, the tankless water heater should resume normal operation. If hot water issues persist, seeking professional assistance is recommended.

Will An Outdoor Tankless Water Heater Freeze?

Outdoor tankless water heaters are more prone to freezing due to their exposure to the elements. However, many outdoor models have built-in freeze protection features such as electric heating elements or recirculation systems. Additionally, using a recess box, which is a protective enclosure installed around the unit, can provide extra insulation and shielding against freezing temperatures.

Can I Cover My Tankless Water Heater?

You can cover your tankless water heater to provide additional protection against freezing and the elements. However, it’s important to use a breathable cover that allows proper airflow and does not obstruct ventilation. Follow the manufacturer’s recommendations and guidelines for covering your specific tankless water heater model.

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