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Unlike traditional tank-style water heaters, tankless water heaters don’t store hot water. This means tankless models have a greater risk of freezing up in cold weather.
Key Takeaways:
- Do not unplug the unit: Your Navien tankless heater requires electricity to run its internal freeze protection mode. Keep power and gas valves ON.
- Power outage warning: If you lose electricity during a freeze, the internal protection fails. You must drain the unit immediately or install a battery backup.
- Running water helps: During extreme cold, keeping a "pencil-width" stream of hot water flowing from a faucet can prevent internal freezing.
- Watch the garage: Units installed in garages or outdoors are at the highest risk; ensure all external pipes are insulated, and drafts are sealed.
- Warranty alert: Damage caused by freezing is not covered by our manufacturer warranty, so preventing your tankless unit from freezing is critical.
Frozen water can damage your tankless water heater, but there are simple precautions you can take to keep your tankless hot water heater from 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.
- Use hot water on a regular basis to keep the pipes warm.
Winterizing a Tankless Water Heater
To winterize your tankless water heater:
- Drain the water heater
- Disconnect the power and gas supply
- Shut off the cold water supply
This will help protect against freezing while you’re away. Find instructions for draining Navien tankless water heater in your user's manual.
Protecting Outdoor Tankless Water Heaters
Tankless hot 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. Insulate pipes to keep freezing temps from reaching water lines.
Protecting 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.
In freezing temperatures, condensate produced by a condensing tankless hot water heater can freeze inside the drain line, which can cause leakage, operation issues or shutoff.
To help keep 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.
A direct vent system minimizes air movement in the water heater and helps keep the condensate drain and other components from freezing.
Navien Tankless Water Heater Freeze Protection
Navien tankless water heaters have an optional recirculation mode to be used for freeze protection.
The recirculation mode should help prevent the water heater from freezing, even if the air intake duct isn't vented directly. Note that this function requires electricity to operate.
All 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.
Signs Your Tankless Water Heater Is Frozen
Here’s how to tell if your tankless water heater is frozen:
- Zero flow from the hot tap: If you turn on the hot water and absolutely nothing comes out (not even cold water), but the cold water tap works fine, your water heater inlet or outlet pipes are likely frozen.
- A trickle of water: If the flow is drastically reduced to a thin stream, ice is likely forming inside the pipes, blocking the path.
- Error codes on the display: Look for codes related to ignition failure (E003) or air intake blockage (E110). If the condensate drain line freezes, the unit thinks the exhaust is blocked, triggering one of these shutdown codes.
- Strange noises: Loud rumbling, popping, or banging sounds when the unit tries to fire up usually indicate ice is obstructing the internal mechanisms or water flow.
- Visible frost or cracks: Check the exterior of the unit (if mounted outside) and the pipes leading into it. Bulging copper pipes or visible frost on the valves are clear indicators.
Thawing a Frozen Tankless Water Heater
If hot water will not flow and you suspect your tankless water heater is frozen, follow these steps:
- Press the Power button on the front panel to turn off the water heater.
- Close the gas valve.
- Open the hot water faucet that is closest to the water heater.
- Use a hair dryer or a portable electric heater to heat up both the primary and secondary heat exchangers.
- Check every few minutes to see if water is running at the open faucet.
- When the water starts flowing again, check the water heater and piping for leaks. If you detect any leaks or the water heater is not operating properly, contact an authorized technician or licensed professional.
Frozen Tankless Water Heater FAQ
Will running water prevent freezing?
Yes, but it requires a specific technique. While a slow drip prevents pipes from bursting, for a tankless unit, you usually want a stream about the width of a pencil. This ensures enough water velocity to prevent freezing inside the heat exchanger, even if the unit isn't firing up to heat the water.
Will freeze protection work if the power is out?
No. If the power fails, the freeze protection function cannot operate. If you expect a power outage during a freeze, you should drain the unit immediately.
Why is my unit showing an error code even after it thawed?
Your unit likely stored a failure to ignite (E1003) or blockage code (E110) from when it was frozen. You usually just need to reset the unit by pressing the reset button on the control panel to clear the code and resume normal operation.
When should I call a professional?
While some minor freezes can be thawed with patience and a space heater, you should stop immediately and call a licensed plumber or technician if:
- Water is leaking from the unit's casing: If water is dripping from the bottom of the tankless unit itself
- You smell gas: If you smell sulfur or rotten eggs while trying to thaw the unit, turn off the gas supply immediately, leave the house, and call a professional.
- Error codes won’t clear: If you have successfully thawed the unit and performed a hard reset, but the error code remains, the freeze may have damaged a sensor, the computer board, or the flow switch.
- The freeze is inaccessible: If the frozen section appears to be inside a wall or in a crawlspace you cannot safely reach with a heat source, do not risk using open flames or makeshift heating tools. Professionals have specialized equipment to thaw pipes inside walls safely.
Can a tankless water heater freeze in the garage?
Yes. In fact, garages are a common location for frozen tankless units because homeowners assume they are "indoors" and therefore safe. Garages often have vents or poorly sealed doors. A draft hitting the unit's heat exchanger can act like a blast chiller. To help prevent a frozen tankless water heater in your garage, seal drafts, make sure all the piping is insulated with foam, that the unit is plugged in to a working outlet so freeze protection can work, and leave a hot water tap in the home dripping if temperatures are expected to drop below freezing in the garage.
If my tankless water heater froze, is it ruined?
Depends. Navien tankless units have stainless steel heat exchangers, which are incredibly durable under normal conditions, but they have tubes that can burst if the freezing water inside them expands. If you see water leaking from the bottom of the casing after it thaws, the internal pipes have likely burst.
Why did my unit freeze if it has built-in freeze protection?
Internal freeze protection helps keep the water inside the unit warm. But it won’t protect the external pipes leading to the unit, nor will it protect the condensate drain line, if you have a condensing model. If your condensate line freezes, the unit will shut down to protect itself, leaving the water inside vulnerable to freezing.
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