USA Water quality is supported by its audience. If you buy something through our links, we may earn money from our affiliate partners. Learn more

How to Thaw a Frozen Tankless Water Heater? – 6 Steps

Fact checked by Stephen Conklin

how to thaw a frozen tankless water heater

Some homeowners wonder how to thaw a frozen tankless water heater. It is a valid concern, even with recent technological advances that prevent freezing.

Insulation and location selection can only go so far in protecting your appliance from harsh weather. Homeowners must be ready to address any water heater freezing concerns.

Continue reading because we will help you learn how to unthaw a tankless water heater in only six easy steps.

Table of Contents

Step-by-Step to Thaw a Frozen Tankless Water Heater

What to Prepare

You only need one or two things to defrost a tankless water heater – a space heater or a blow dryer. Most folks use the latter because it is handier.

A screwdriver and insulating materials (i.e., water heater blanket and heat tape) will also be useful.

Step 1. Disconnect the tankless water heater from its power source.


Some tankless water heaters use electricity, while others are gas-powered. Either way, there might be residual heat in the water heater. This heat could injure you if you keep the device turned on.

So, switch off the electric tankless water heater’s circuit breaker at the electrical panel. For gas units, shut off the gas supply valve.

Step 2. Remove the tankless water heater cover.

Grab a screwdriver or an appropriate hand tool to loosen the fasteners on the tankless water heater’s cover.

This step is necessary because you will want to examine the water heater’s interior components for frozen sections and other signs of damage.

Most tankless water heater covers have silicone or rubber gaskets forming a seal around the device. Be careful when removing the gasket to protect its integrity.

Place the cover, fasteners, and gasket in a container to avoid losing them.

Step 3. Assess the tankless water heater’s internal plumbing network and surrounding pipes.


Visually inspect the tankless water heater’s interior components for signs of frost. If none are visible, you can run your fingers on surfaces to check if they are cold.

Inspect also the water pipes outside the tankless water heater. Check for signs of cracks in the pipes.

Do not thaw outdoor tankless water heater units with a burst or cracked pipe.

Your next move should be to call a licensed plumber in your area. Leaks can occur in these sections if you proceed with the water heater defrosting.

Step 4. Slightly open a hot water faucet.

Opening a hot water faucet allows melted ice to flow through the pipes and out the tap. It also prevents backward pressure that can damage the tankless water heater or burst a water pipe.

Step 5. Thaw the tankless water heater.


Grab the blow dryer and turn it to the highest heat setting. It should warm the water pipes and heater components enough to melt the ice.

  • Do not use a heat gun because its heat production is higher than a blow dryer. It can damage the tankless water heater’s components if you’re not careful.
  • Hair blowers or blow dryers produce 80 to 140-degree Fahrenheit heat. Meanwhile, heat guns deliver 200 to 1,000-degree Fahrenheit hot air.

Keep the blow dryer moving to facilitate more efficient thawing and minimize damaging the tankless water heater.

Ask someone to check the open hot water faucet and see if the water is dripping, indicating the defrosting process is working.

You might also want to turn on the tankless water heater and see if it warms the water passing through the pipe network.

Continue applying heat until frost has disappeared and the faucet’s flow is no longer weak.

Step 6. Apply insulation to prevent future freezing.

Turn off the tankless water heater and allow it to cool. This step is necessary to avoid burning yourself when applying insulation and heat tape.

Check the tankless water heater for missing insulation and replace these with an appropriate material.

Wrap heat tape around the pipes (both inside and outside the tank) to insulate them.

Replace the tankless water heater’s cover and secure the fasteners. Place a space heater next to the appliance to aid in freeze prevention.

Reestablish power to the tankless water heater and enjoy hot water in the winter.

Why is the Tankless Water Heater Freezing?

Thawing a tankless water heater requires understanding why the device freezes in the first place.

Water freezes when individual water molecules slow down because of a temperature drop. The molecular movements are so sluggish that water molecules stick to each other, forming an ice crystal.

These crystals solidify into ice as temperatures drop to freezing point (32 degrees Fahrenheit).

Tankless water heaters freeze when water is within their internal components, and the ambient temperature is low enough to cause water molecules to crystallize.

Although modern tankless water heaters have built-in freeze protections, these technologies have limited brand-specific temperature thresholds (i.e., minus 4 or minus 22 degrees Fahrenheit).

Ambient temperatures lower than the water heater’s freeze threshold can cause the device to freeze. For example, minus-30-degree weather will freeze a tankless water heater with a minus-4-degree limit.

Power outages can also affect these technologies’ performance, leaving you with a frozen water heater.

Tips to Prevent It


Here are several tips to keep a tankless water heater from freezing and help you avoid the hassle of unfreezing tankless water heater units.

  • Choose a warm and draft-free location for your tankless water heater to protect it against freezing. Consider heated spaces when installing a tankless water heater.
  • Drain the water heater to eliminate standing liquid within its internal components. Do this action when you don’t use the appliance for extended periods. You will never unfreeze a hot water heater again with this trick.
  • Ensure to plug the water heater into an electric outlet to keep its freeze protection running, even though the water heater is off. You might want to connect it to a backup power generator or battery to keep it operational even during an electricity outage.
  • Open a hot water faucet farthest from the tankless water heater, only slightly, so that a tiny amount of liquid can flow out. This trick keeps the water moving, preventing it from crystallizing and turning into ice. There is no need to power on the water heater for this technique.
  • Insulate the tankless water heater with a fiberglass or aluminum foil-foam blanket. You can also wrap heat tape around water pipes supplying the tankless water heater.
  • Install a water heater recirculation system to help channel some hot water through the internal pipe network. This technique keeps the pipes and water heater warm enough to prevent ice formation.

Frequently Asked Questions


What happens if my tankless water heater freezes?

A frozen tankless hot water heater can damage the water heater’s internal components.

Freezing occurs when standing water forms crystals because of low ambient temperature. The crystals solidify as the temperature continues to drop with zero water movement.

Ice expands and pushes against the tankless water heater’s interior elements.

Although many brands have tankless water heater freeze protection, these technologies have limitations.

First, they require electricity, which could be a problem in a power outage. Second, freeze protection technologies have limited temperature thresholds (i.e., they can only protect the water heater from freezing up to a certain temperature).

At what temp does a tankless water heater freeze?

The temperature at which a tankless water heater freezes depends on the brand and any existing freeze protection technology.

For example, Rheem tankless water heaters only start to freeze at minus-30 degrees Fahrenheit.

Meanwhile, a minus-four degrees Fahrenheit outdoor temperature can turn a Rinnai tankless water heater frozen. Indoor units are more cold-resistant, withstanding up to minus-22 degrees Fahrenheit before freezing.

You might want to check your tankless water heater’s manual for its operating temperatures, especially its lowest threshold (i.e., minus 20 degrees Fahrenheit).

How do I know if my tankless water heater is frozen?

You will know your tankless water heater is frozen if you live in a cold climate and the water remains cold even though the water heater is running.

You might also hear odd sounds from the water pipes, mostly from water passing through ice-narrowed sections or ice chunks hitting the tubes’ interior.

No hot water from the shower or hot water faucet can indicate a completely frozen pipe or tankless water heater. Ice could block the passageways, preventing water from getting warmed and passing through.

You might want to unfreeze tankless water heater units before resuming hot water use.


Mastering how to thaw a frozen tankless water heater is as straightforward as observing the six easy steps outlined above. You only need a few tools to execute this activity, although a keen eye for signs of freezing and associated damage can help.

Hot water is essential for many families, especially in the winter months. And although some brands have anti-freeze technologies, these systems can only do so much. Homeowners must be proficient in defrosting their tankless water heaters.

5/5 - (5 votes)