How To Thaw Tankless Water Heaters (6-Step Guide)

Licensed Inspector Arie Van Tuijl
Licensed Inspector Arie Van Tuijl

🕖Last Updated On May 10, 2022

If you want to thaw out a frozen tankless water heater safely and quickly, you are in the right place!

In this guide, you will learn:

  • How to defrost tankless water heaters with a simple hair dryer!
  • Why you need to open up a faucet when thawing it
  • Preventative equipment to stop freezing
  • And more!
how to thaw frozen tankless water heater

Do you have a frozen tankless water heater and need to quickly thaw it out?

Most people don't know that frozen tankless units can be easily thawed with a simple hair dryer! A hair dryer is perfect because it is gentle enough that it won't cause damage if you are careful.

A heat gun isn't recommended because it may damage some of the electrical components of the tankless heater due to the high heat.

Keep reading to learn the 6 steps on how to thaw a tankless water heater!

What You Need To Know About How To Thaw A Frozen Tankless Water Heater

Thawing a frozen tankless water heater is pretty simple to do even for inexperienced homeowners.

It really just takes a screwdriver, a hair dryer, and waiting 15-min to 45-min!

As soon as the pipes start to thaw, the tankless unit should turn on again, and hot water will flow out of the faucet. But once it is thawed, make sure that there is adequate heat tape and insulation so it doesn't freeze again!

Typically, tankless water heaters have some freeze protection but not all do. If your climate sometimes gets freezing weather, you need to make sure that your unit has enough heat tape and insulation to avoid freezing.

Read Also >> How To Reduce Noise From A Tankless Water Heater?

Supplies You'll Need To Thaw Tankless Water Heaters

  • Hair Dryer - A hair dryer will be needed to slowly defrost the frozen piping.
  • Screwdriver - A simple screwdriver will be needed to remove the screws on the tankless water heater cover in order to remove it.
  • Heat Tape - Heat tape will be needed to prevent future pipe freezing.
  • Insulation - Pipe insulation is needed to stop freezing pipes and it is installed over heat tape.

How To Thaw Tankless Water Heaters (6-Step Guide)

  1. Remove The Tankless Water Heater Cover
  2. Inspect The Interior And Surrounding Piping Of The Tankless Water Heater
  3. Open Up A Sink Faucet With A Steady Drip With Hot Water
  4. Use A Hair Dryer To Slowly Thaw Out The Frozen Piping
  5. Keep Using Hair Dryer Until Hot Water Flows Out of Faucet
  6. Prevent A Frozen Tankless Water Heater With Heat Tape And Insulation

Step 1 - Remove The Tankless Water Heater Cover

Remove the tankless water heater cover so you can get access to the interior pipes.

There will likely be a few screws that need to be removed, and there may be a rubber gasket that comes off. Be careful not to lose any screws or misplace the gasket.

Step 2 - Inspect The Interior And Surrounding Piping Of The Tankless Water Heater

Inspect the interior and exterior plumbing of the tankless water heater.

Before doing any thawing of the pipes, it is a good idea to try to determine where exactly is the frozen piping.

The frozen pipes may be just inside the tankless water heater, but it may also include some of the piping on the outside of the unit. Homeowners can use their hands to determine what exactly is frozen by touching the pipe.

It is also a good idea to keep an eye out for any cracked or busted piping. If there is any cracked pipe, once you start thawing the tankless water heater, there will be leaks.

Read Also >> What Size Tankless Water Heater Do I Need?

Step 3 - Open Up A Sink Faucet With A Steady Drip With Hot Water

Open up a faucet on the hot side just enough for a steady drip.

This step is important because once the tankless water heater starts to thaw, it will allow water to flow. If you don't do this step, it may cause pressure in the system, and even a ruptured pipe.

And once hot water starts to flow out to the sink, you will know that the tankless water heater has thawed!

Step 4 - Use A Hair Dryer To Slowly Thaw Out The Frozen Piping

Use a hair dryer to that out the frozen piping without damage.

A hair dryer puts out enough heat to thaw the frozen tankless water heater, but not enough to cause damage. Anything stronger like a heat gun may damage the tankless water heater and it isn't recommended.

Use the hair dryer and keep it moving around the around of frozen piping.

Don't keep the hair dryer in one place! Keep it moving in a circular fashion.

It usually takes anywhere from 15-min to 45-min to thaw out a tankless water heater with a hair dryer.

Read Also >> What Are The Best Condensing Tankless Water Heaters?

how to thaw frozen tankless water heater (1)

Step 5 - Keep Using Hair Dryer Until Hot Water Flows Out of Faucet

Use the hair dryer to thaw out the piping until water flows on the hot side from the sink.

This is the same time that the tankless water heater should kick on and heat the water.

Basically, you will have to keep thawing the pipes with the hair dryer until the full flow of hot water is restored.

Step 6 - Prevent A Frozen Tankless Water Heater With Heat Tape And Insulation

Stop a tankless water heater from freezing with heat tape and insulation.

Even though most modern tankless water heaters have freeze protection, it sometimes isn't enough. If there is missing heat tape and insulation on the inside of the tankless unit, or on the surrounding pipe, it is essential to add these items to prevent future freeze events.

And if the tankless water heater is on the inside in an unconditioned space, you can install a space heater to help prevent freezing as well.

How Do You Unfreeze A Tankless Water Heater?

Unfreezing a tankless water heater involves using a hair dryer to slowly and safely thaw out the pipes.

Once the pipes start to thaw, water will trickle out of the faucet on the hot side and the unit will kick on.

On average, it takes 30-60 minutes to thaw a frozen tankless water heater.

Read Also >> How To Flush A Tankless Water Heater?

What Happens If Your Tankless Water Heater Freezes?

A tankless water heater frozen will totally stop the operation of the unit (and no more hot water).

Frozen pipes inside the tankless water heater can also damage internal components like the heat exchanger. It is essential to quickly thaw out a frozen tankless water heater before damage occurs.

Homeowners should take preventative steps during freeze events such as installing heat tape. Insulate the pipes as well which acts as a second level of protection and installed over the heat tape.

Why Did My Tankless Water Heater Freeze?

Outdoor and indoor tankless water heaters may freeze if there isn't satisfactory protection from plunging temperatures that drop below freezing.

Sometimes cold air will even travel down the tankless water heater vent and freeze the pipes.

Even though most units have freeze protection, the pipes leading to the tankless water heater also need to have heat tape and insulation to keep pipes from freezing.

Read Also >> How To Adjust Temperature On A Rinnai Tankless Water Heater?

What Happens If Your Hot Water Heater Freezes?

If your hot water freezes, it may freeze the pipes inside the unit or nearby on the outside. 

And once the pipes are frozen, the ice expands and may cause pipe ruptures.

Of course, a tankless water heater freezing will shutdown the hot water flow to the home, and it may even damage the heat exchanger.

Should I Turn Off Water Heater If Pipes Freeze?

If homeowners can't immediately thaw the tankless water heater, then they should at least turn off the main water valve.

If any if the pipes burst, it may cause flooding damage.

Any water damage can be mitigated by turning off the main water valve to the home.

Final Thoughts On Thawing A Frozen Tankless Water Heater

There is nothing more annoying than a tankless water heater not working in cold weather.

Luckily, these tankless units can be thawed out with a simple hair dryer! And hair dryers are safe to use since the heat output isn't very high. Just don't forget to open up a hot water faucet to allow a steady drip while using the hair dryer to heat the area.

And once it's thawed, it's essential to prevent future freezing with adequate heat tape and insulation.

I hope you enjoyed this Home Inspector Secrets guide!

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