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June 26, 2023

Preventing a Frozen Tankless Water Heater

Unlike traditional tank-style water heaters, tankless models don’t store hot water. This means tankless models have a greater risk of freezing up in cold weather. Frozen water can damage your tankless water heater, but there are simple precautions you can take to avoid this.

Whether you have an indoor or outdoor unit, use these tips to reduce the risk of freezing:

Do not unplug the power supply cord, except for routine maintenance. Your Navien tankless water heater has a freeze protection function that requires electricity. The freeze protection function will operate whether or not the front panel is powered on or off but the power toggle switch and power cord must be ON and connected.

If your building is prone to frequent power outages, consider a battery backup or generator when freezing weather is predicted.

Do not close the gas valve, except for routine maintenance. Closing the gas valve will limit additional freeze protection.

If you must disconnect the power or gas for an extended period, drain the water heater.

Insulate water pipes connected to the water heater.

To winterize your tankless water heater, drain the water heater, disconnect the power and gas supply, and shut off the cold water supply. This will help protect against freezing while you’re away.

Keep reading to learn additional freeze-prevention tips specific to indoor and outdoor units.

How to Protect Outdoor Tankless Water Heaters

Tankless water heaters installed outdoors have a higher risk of freezing. Do not install a tankless water heater outdoors in areas prone to freezing temperatures.

Choosing a sheltered exterior location can also help prevent freezing issues. If possible, install your outdoor tankless water heater where it will be sheltered from wind, or build an enclosure that blocks the wind. Install a pipe cover to conceal and protect the gas, water and power connections.

How to Protect Indoor Tankless Water Heaters

Tankless water heaters installed indoors can freeze if there’s a power outage, or if there’s back drafting caused by negative pressure in the building. Back drafting draws cold air into the unit via the exhaust pipe which can cause internal components such as the heat exchanger coil or condensate drain to freeze.

To help prevent your indoor tankless water heater from freezing, use a direct vent exhaust & intake system. Both the exhaust vent pipe and the air intake pipe should be connected directly from the collars on the top of the water heater to the outdoors. This type of vent system minimizes air movement in the water heater.

Navien Tankless Water Heater Freeze Protection

Navien tankless water heaters have an optional recirculation mode to be used for freeze protection. This mode should help prevent the water heater from freezing. Note that this function requires electricity to operate.

All of Navien gas tankless water heaters (natural gas or liquid propane) include the freeze protection feature.

Whenever your tankless water heater will not be used for an extended period, drain the water heater. Any standing water in the unit will expand if it freezes, which could cause damage.

Damage caused by freezing is not covered by the Navien limited warranty. We strongly recommend taking every precaution to prevent freezing issues. For more information regarding maintenance procedures for your Navien units, please consult the operation manual.

Learn more
Simple tips for maintaining your Navien tankless water heater

Using tankless water heaters in cold climates

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