How to Defrost a Tankless Water Heater – A Beginner’s Guide

Tankless water heaters are one of the best inventions made for winter. Not only do they provide a continuous supply of hot water, but they also rarely freeze up. However, in certain cases, a tankless water heater can freeze. 

This guide elaborates on the risks that come with it, why it gets clogged with ice, and how to defrost a tankless water heater. Keep reading, as we’ll also share a few preventative measures.

Can a Tankless Water Heater Freeze?

Yes, a tankless water heater has the tendency to freeze — no matter if it’s placed outside or indoors. Here are a few reasons for this:

  • The antifreeze protection coating on the system is thin or worn out
  • The temperature has fallen below -5°F to -23°F
  • Lack of insulation on the pipes
  • The power source is irregular or destabilized

Tankless water heaters are designed to withstand freezing temperatures, so if they freeze, it’s probably due to the ill-maintenance of the system.

What Happens if a Tankless Water Heater Freezes?

If a tankless water heater freezes, the entire system could halt – from the source that brings in cold water to the pipes that carry the heated water toward the sink. This means you won’t receive hot water until the pipelines are unfrozen.

Also, if the unit isn’t thawed out soon enough, the ice could expand and cause significant ruptures in the pipes. Working overtime can also damage the heat exchanger

This ultimately leads to extra expense on restoration or even installation of a new tankless water heater. To avoid such a hassle, insulate the tankless water heater and connect a power stabilizer if you’ll be out for the winter.

How to Defrost a Tankless Water Heater?

No matter how the tankless water heater got frozen, it’s essential to melt the ice as soon as possible. Don’t worry – the procedure requires little technical knowledge and is primarily tool-free. Here’s a stepwise guide on how to defrost a tankless water heater:

Step 1: Mark the Areas of Concern

First, loosen the cover from the water heater using a screwdriver and place it somewhere safe. 

Then, inspect the entire unit and mark where the ice is clogged by running your hand over the system. If you caught it early, it’s likely just the water heater that feels extra cold and needs to thaw. 

Also, check the plumbing, and ensure to include all pipelines. If there’s a burst, tape it shut before melting the ice to ensure there isn’t any leakage.

Step 2: Thaw Out the Frozen Areas

Once you’ve marked the areas of concern, open the furthest tap to a steady stream of hot water. This way, when the tankless water heater starts thawing, the water will start flowing toward the sink while melting any residual ice.

Next, apply heat indirectly using a hair dryer or a space heater. Be sure to keep it moving clockwise so hot air reaches all affected areas, a constant burst of air to one point can overheat that section.

Water should start flowing from the open faucet within 15 to 45 minutes. If it doesn’t, the entire unit is frozen, unfortunately. Here’s what you should do then:

Detach the Entire Unit

inside a water heater

Turn off the power source – the gas or electricity supply and the water supply pipe that fills up the heater. Disconnect the entire unit and place it in an open field like a lawn or a garage. 

Keep in mind that at this moment, there is a risk of the tankless water heater bursting open or a pipe rupturing which will cause a leak. So, an open field is a must.

If direct sunlight isn’t available, place a room heater nearby and turn it up to thaw the unit. Once it starts to melt, open the drain valve, usually found at the bottom of the tankless water heater – melted ice will begin to flow. Once it stops, attach the system back again.

What Not To Do When Thawing Out a Frozen Tankless Water Heater?

Thawing out a frozen tankless water heater undoubtedly requires a heat source that can easily melt the ice. 

You could simply place the unit in direct sunlight, which will do the trick. However, if you’re short on time or the system risks bursting, you could use a hair dryer to liquefy ice in the pipes. 

You shouldn’t use a heat gun or similar hot air appliances that can reach up to 1200 degrees Fahrenheit. This is because they can easily damage the pipelines or even melt the structure if not handled carefully. 

How Can You Stop the Tankless Water Heater From Freezing?

Although it doesn’t occur as often, the possibility of a tankless water heater freezing is never zero. Not to worry, there are a variety of ways to prevent an ice clog, and some of the best tips are detailed below:

Place the Water Heater in Direct Sunlight

The easiest tip to remember when installing a tankless water heater is to ensure the unit is set under direct sunlight or in a warmer environment. This way, the freeze protection coating on the unit can easily keep the hot water running.

Insulate the System

Since it’s a universal measure of preventing adverse reactions, insulating the tankless water heater covers the exposed areas and protects against freezing. Be sure to place more focus on the pipes near-ground or underground. 

There are three types of insulation available for heating pipes:

  • Polyethylene coat which is eco-friendly, versatile, and works with any season. 
  • Fiberglass insulation has one of the best survival rates under extreme weather but is rather expensive.
  • Heat tape is plugged in to get the pipe warm and is one of the most inexpensive insulators available.

Run Hot Water Through a Tap

The most effortless unfreeze tip here – run the tankless water heater all night long and keep a faraway tap open to release the hot water. This is an effective way of dealing with frozen pipes. Although it takes longer, the water heater works at its own pace, which preserves the integrity of the other parts.

Drain the Tankless Water Heater

A tankless water heater will most likely freeze when it’s filled with water. So, before you move out of the shelter or travel long distances, empty the heater by keeping the furthest tap slightly open. This way, the entire unit is drained of ice from the source to the sink. 

Keep the Anti-Freeze System Running

Every tankless water heater comes with a freeze-protection coating in its pipelines. It works to prevent ice from crystalizing inside and does the preventative work for you. But, it requires electricity to run. So, ensure the water heater is plugged in at all times – even when powered off.

Keep a Power Stabiliser on Standby

Because a tankless water heater needs a constant source of gas or electricity to run, the power source it’s connected to must be reliable enough to run consistently. It must also have a battery backup, power stabilizer, or a drain-down solenoid in case a breakdown occurs.

Frequently Asked Questions

Do You Have to Winterize a Tankless Water Heater?

Yes, you need to winterize a tankless water heater in the fall to prepare for the colder months and before shutting down its power source in the summertime. Winterizing a tankless water heater helps protect the system from bursting pipes and unexpected leakages. 

Does Cold Weather Affect a Tankless Water Heater?

Yes, cold weather does affect a tankless water heater. The lower the temperatures, the longer it’ll take for the water to heat up. 

Also, it’s rare and usually because of ill-maintenance, but tankless water heaters can freeze too. This places the water pipes and heating system in jeopardy. So, be sure to check on it regularly.

Can I Preheat Water Before It Goes Through a Tankless Water Heater?

No, it isn’t a good idea to preheat water before it goes through a tankless water heater. This is because the entire system is designed to provide a never-ending hot water supply throughout winter. Adding warm water beforehand just adds unnecessary effort to the mix.


Similar to essential heating, ventilation, and air conditioning (HVAC) system maintenance, a tankless water heater also needs a little extra attention to perform effectively and efficiently through winter. 

A major way to achieve this is to know how to defrost a tankless water heater. Aside from this, it’s crucial to apply preventative measures to enjoy hot water throughout the cold season.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.