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How To Keep Your Tankless Water Heater From Freezing

Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

Tankless water heaters are becoming increasingly popular because they save energy and reduce carbon emissions.

They also provide hot water instantly, without having to wait for the boiler to come back on after being switched off.

However, while many of us understand the basics of the tank-style heater, the new tankless models can be confusing.

That means if maintenance is needed, or your tank develops a fault, you may not know what to do.

When cold winter weather starts, and you need the heater more than ever, you may not know how to prevent the tank from freezing. Or if it can even freeze in the first place. 

A tankless water heater can freeze, although it’s a rare occurrence.

Most tankless water heaters are built with electric freeze protection, so when temperatures dip low, the heater stays operational.

However, if the power cuts out, or there’s a period of extreme low temperatures, the heater can still freeze.

Find out how to prevent it with this guide.

Can Tankless Water Heaters Freeze?

Yes! Even though there is no tank, a tankless water heater can still freeze if the temperatures drop low enough and precautions aren’t taken.

When there’s standing water left inside the heater, the low temperatures can cause this to freeze. 

Freezing water doesn’t just turn solid — it expands. As the water turns to ice it grows, putting pressure on the interior of the heater, and potentially causing serious damage.

If a tankless water heater freezes, the repairs can be costly.

However, tankless water heaters are typically prepared for freezing temperatures.

Most come with built-in freeze protection.

When the temperature drops between -5 and -22 degrees Fahrenheit, an electrical component will kick in, and prevent the delicate internal parts from freezing.

This can be found on most indoor and outdoor tankless water heaters.

But this freeze protection only works in a limited capacity. It won’t protect against all types of freezing conditions.

Extended periods of freezing weather might overpower the internal heater, causing the parts to freeze.

Also, the freeze protection requires electricity to work.

In the event of a power outage, or another issue with the power source, the internal heating will lose electricity.

The tankless water heater will then be vulnerable to freezing. 

To prevent freezing, it’s best to take some extra preventative action. 

Tips On Ensuring Your Tankless Water Heater Won’t Freeze

How To Keep Your Tankless Water Heater From Freezing

A frozen tankless water heater is a nightmare to fix, and will often need to be replaced.

The ice can damage the internal components, and a replacement can be less expensive than a repair.

To avoid this, take preventative measures. It’s rare for a tankless water heater to freeze, but it can happen. 

These simple advance measures act as a back-up in case there’s an issue with the built-in freeze protection.

By following these actions, you can keep a consistent supply of hot water, and avoid dealing with expensive repairs.

If you’re worried about your tankless water heater freezing during extreme cold weather, here are some tips to help keep it safe:

Install The Tankless Water Heater In A Sheltered Area

The first step to preventing freezing comes with the insulation.

Tankless water heaters are often installed outdoors, although they are sometimes set up within the house.

A tankless water heater should ideally be installed in a sheltered area that has good insulation.

The surrounding air will be warmer, which reduces the risk of freezing during cold nights.

It’s important to note that it isn’t always possible to install the heater away from the cold.

Some locations don’t have access to a suitable shelter, or you might not have room for a tankless water heater indoors.

But if you can find somewhere sheltered where installation is possible, then it’s worth considering.

Tankless water heaters can be installed both indoors and outdoors.

If there’s an indoor area suitable for the tank, we recommend installing it here.

If you have to go outdoors, look for a place away from the wind.

Find an area with a reduced wind level, or add fencing to block the wind as much as you can.

Run Water Through The Water Heater

Tankless water heaters can freeze because there’s water left standing still.

To reduce the risk of this happening, you can run a continuous, gentle stream through the heater.

The water keeps moving, which makes it less likely to freeze.

Turn a faucet on at a low level, somewhere out of the way. Only about 0.2 gallons per minute needs to be running to prevent freezing.

As this works alongside the built-in freeze prevention, this should only need to happen during incidents of extreme cold.

You will see a slightly higher water bill, but the overall cost should still be significantly less than the cost of a repair or replacement.

To avoid wasting all the water, you can collect some run-off in a bucket. 

Keeping the water running can be impractical, but it’s only necessary during the worst weather, or if the power is down.

During most periods of cold weather, the tankless water heater won’t be at risk, as the freeze protection will be working.

You only need to run the water when you think the heater is vulnerable. 

Back Up The Built-In Freeze Prevention

The built-in freeze protection system is designed to kick in when temperatures drop below a certain degree Fahrenheit.

When this happens, the system kicks into gear. It uses electricity to melt ice inside the tankless water heater, and keep things nice and warm.

However, if these systems run out of power, then the tankless water heater can freeze. And freezing temperatures can lead to power cuts.

The best way to navigate this is to ensure your tankless water heater is hooked up to a separate generator.

This way, if the power goes off, the electric protection system won’t go down with it. 

If you have a back-up generator already installed, make sure one of the systems links to the tankless water heater.

If you don’t have a generator system, consider purchasing a small and portable option to use in these emergencies.

If there are warnings of extreme weather, you can set up the generator in advance. 

This tip will help keep the electric freeze protection working even during a power outage.

However, freeze prevention can only do so much. If the temperature can get below -22 degrees Fahrenheit where you live, then consider following our extra precautions. 

Winterize When Necessary

Winterizing involves removing any remaining water from the water heater, and shutting everything down.

This will reduce the risk of freezing by removing the standing water that you might not realize is trapped in the heater. 

There are two occasions when you might want to winterize your tankless water heater.

First, when the power is out. Second, if you’re away from the water heater over winter. These are both periods when non-use might lead to freezing.

Tankless water heaters will often include solenoid valves as part of the freeze protection.

These valves are open when not powered, and closed when powered. If the power goes out, the valves open, and the water can drain.

If your water heater doesn’t come with solenoid valves, consider getting them installed.

How To Drain Your Tankless Water Heater

If you don’t have solenoid valves, you’ll need to drain the water heater yourself.

  1. Shut down the gas supply, cold water supply, and the temperature control panel.
  2. Disconnect any electrical power sources.
  3. Inside the house, open a hot water tap to release the pressure, catching the water in a bucket.
  4. Take the drain caps off the cold and hot water isolation valves.
  5. Open both valves.
  6. Take the cold water inlet filter and drain caps from the water heater base.
  7. With the tank shut down, you might choose now to do some maintenance.

Add A Hot Water Recirculation System

How To Keep Your Tankless Water Heater From Freezing

A hot water recirculation system is most commonly used to ensure a quick supply of hot water to an area of the home, but they can also help prevent freezing.

By consistently moving the water around the pipes, the water heater stays engaged, and the water can’t sit and freeze.

However, a hot water recirculation system can be expensive. For many homes, the cost of installation won’t be worth it.

This option is only really worth considering if you have other needs for a hot water recirculation system.

A hot water recirculation system delivers hot water quickly to fixtures away from the heater, so it’s most useful on large properties.

Pipe Insulation

Insulating the pipes can help prevent freezing. You can insulate all or just some pipes.

There are different types of insulation available, including heat tape, polyethylene insulation, and fiberglass insulation. 

Pipes that pass outdoors or are in an uninsulated area should be given extra protection.

You should also winterize your pipes if you plan on leaving a house unattended during cold months.

Insulating pipes involves adding a layer of protection to the outside of the pipe.

Before cold weather hits, either install insulation, or check the state of the current insulation.

Check the insulation on all the pipes leading into the water heater. Make sure it’s in good shape, and remove and replace any damaged sections.

Insulating pipes does more than just reduce the risk of freezing.

Well insulated pipes can deliver hot water quicker, and keep water hot so you can reduce the temperature settings. 

What Do I Do If My Tankless Water Heater Freezes?

When you wake up on a cold winter morning only to find there’s no hot water, it can be pretty worrying.

Winter is when we need hot water most, but it’s also the time when your heater is at its most vulnerable.

Even with electrical freeze protection in place, a tankless water heater can still be damaged by the cold.

But there’s no need to panic. Tankless water heaters can freeze, but it happens rarely.

There are a few steps to take before you need to be thinking of replacements. 

However, if the tankless water heater has frozen, it can be an expensive fix. 

Check The Pipes

Before you assume there’s an issue with the heater, the first thing to check is the pipes.

As pipes don’t have the same smart insulation as the tankless water heater, they’re more likely to freeze. 

First, check where the pipes enter and leave the house. These areas are typically the most exposed.

If none of these sections are frozen, check further along the piping until you can find the issue.

If the pipe is frozen, you must deal with it immediately. Otherwise, the frozen water can expand and crack the pipe.

Open the faucets, so that the water and steam can be released. The running water can also help with the thawing.

Apply heat to the pipe using something like a hair dryer or a heat gun.

If you don’t have anything suitable, soak a towel in hot water and wrap it around the pipe.

When the towel cools down, soak it in hot water and apply again. Never use a blow torch or anything with an open flame.

You can use a space heater, but make sure there’s nothing flammable nearby, and never leave the heater unattended.

To speed up the process, turn on the heat in your house. This will thaw the pipes from the inside.

With both applications of heat, the frozen pipes should be able to thaw quickly.

Check The Tankless Water Heater

If you’ve checked the pipes and can’t find an issue, then it’s time to check the tankless water heater.

Freezing may have happened because the power went out, or you’ve had the heater switched off.

It might also happen if it’s been extremely cold for a significant period of time.

Once you’ve inspected the pipes, head to the heater and open the drain valve.

If the heater is working, a significant amount of water should pour out.

If no water comes out, but the heater is on and appears to be functional, then it might have frozen. 

Tankless water heaters rarely freeze, but it is a possibility.

A frozen water heater can potentially be repaired, but the ice in the components could have caused major issues.

In many cases, it’s more cost-effective to replace the tankless water heater, than to attempt a repair.

With the tankless water heater fixed or replaced, you can get to work making sure the problem won’t happen again.

Insulate the pipes, be careful with installation, and follow our tips above.

Prevention is the best way to deal with a tankless water heater.

By taking these steps, you can maintain your water heater for longer, and enjoy hot running water throughout the winter months.

author avatar
Charlie Hardcastle


On Key

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