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Cold Weather And Your Tankless Water Heater: How To Prevent 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.

Your tankless water heater requires some extra care when the weather gets cold. You should check your water heater every month during the colder months to make sure that it is working properly.

When you’re ready to shut down your summer cabin, you’ll want to make sure that your tankless water heater doesn’t freeze over winter, and that you’ve prepared it for an easy start-up next season.

Tankless water heaters are great because they use less energy than traditional ones. But if you want to make sure your tankless doesn’t freeze, here are some tips.

Can A Tankless Water Heater Freeze?

Tankless water heaters (see also ‘How To Winterize A Tankless Water Heater And Protect The Plumbing System‘) should be kept inside during cold weather. Cold weather can cause problems with tankless water heaters. Some manufacturers offer free freeze protection.

Some water heaters use ceramic heaters to protect themselves from cold temperatures. Ceramic heaters are added to the heat exchangers and other internal parts, and also to the water lines.

When the temperature drops below 32 degrees Fahrenheit, these ceramic heaters start firing up to prevent the internal parts from getting too cold.

Tankless water heaters use sensors to determine when the water should be heated. When the sensor detects that the water is below freezing, the heater cycles on and off to prevent damage to the unit.

Having said that, in certain conditions, yes, a tankless water heater can indeed freeze.

Common built-in protections are only capable of fending off the cold for a little while. Particularly low, sustained temperatures may well freeze your tankless water heater (see also ‘Why Hot Water Temperature Fluctuates In Tankless Heaters? (How To Fix It)’).

Check your owner’s manual for details on your particular tankless water heater (see also ‘ Rheem Tankless Water Heater Error Codes ‘).

How To Prevent A Tankless Water Heater From Freezing

How To Prevent A Tankless Water Heater From Freezing

Tankless heaters are great for hot water because they heat it so quickly, and part of the reason they’re so quick is that they have the water to hand.

But, if you’re going to be gone for an extended period of time, you should drain your tankless heater to prevent it from freezing.

Tankless heaters can be drained manually, but freezing temperatures can cause them to malfunction.

Water heaters can freeze up if proper precautions aren’t taken. Freeze damage to tankless units usually takes the form of ice forming inside the unit, expanding and damaging the inner components.

Solenoid valves are designed to drain water out of the system when there’s a power outage. They’re normally closed, and they need electricity to stay shut.

When there’s a blackout, the valves automatically open, releasing the water inside the tankless heater.

You should check if the heaters are working properly. If the heaters aren’t working, then you’ll need to add more insulation around the pipes or install a new heating element.

Install your water heater in a warm place. This helps prevent freezing during the winter. Use vent terminations with wind resistant features. The location should be far away from prevailing winds.

Drain your water heater as soon as you go away for an extended period of time. Be sure to isolate the water from the heater, using the valve located on both the hot and cold water lines.

You need to make sure the power supply stays charged up.

In case of a power outage, you must also maintain a backup power supply. You may want to consider installing a recirculation system (see also ‘4 Common Hot Water Recirculation System Problems And How To Fix Them’). This prevents the pipes from freezing over.

Protecting External Pipes From Freezing

Pipe insulation is a great way to save money and energy. Talk to your local plumber about how you can get pipe insulation installed.

Your pipes should be insulated to prevent them from freezing. Running a trickle of water through the pipes also keeps them warm.

Wrapping the external pipes with either pipe insulation or a pipe heating wire can protect them from freezing. These pipes should be protected from freezing because they lead to and from the tankless water heater.

Pipe insulation is used to protect pipes from heat loss. You should never put heating cables inside your pipes because they could damage them.

Always follow the manufacturer’s instructions when wrapping or insulating your pipes.

How To Winterize A Tankless Water Heater

Your tankless water heater (see also ‘Tankless Water Heater Vs. Tank‘) is an important part of your home. Winterizing your water heater before going on vacation is a wise decision.

Tankless water heaters are very efficient and cost-effective ways to heat water. However, if there is any chance of cold weather, homeowners should check their tankless water heaters before winter sets in.

Winterizing your tankless water heaters is a great precautionary measure. You should always check your owner’s manual for details about how to do this properly.

Plumbers can be hired to winterize your tankless system. Make sure you check out the warranty before doing anything else.

Also, make sure you know how much it costs to hire someone to winterize your tankless system.

You must check your tankless water heater before winter arrives. Turn off the unit first and then unplug it from the electricity source. Drain the unit’s tank of water. Reduce the water flow rate and disconnect the pipes .

Cover the intake and exhaust vents with plastic or tape. Install an anti-freeze device in the intake pipe.

You can prevent damage by keeping the temperature inside your water heater above 50 degrees Fahrenheit.

Venting the system is also very important. If you don’t do this correctly, then you might get problems with your tankless water heater. You should also make sure that you clean out the vents regularly.

Prepare For Freezing Weather

Water shutoffs are important because you could lose power during a storm if there isn’t enough pressure to turn off your water.

Keep your shutoff valves clear of debris and make sure everyone in your household knows where they are located.

Outside faucets should be turned off. All connected hoses and faucet pipes should be removed. Sprinkler systems should be drained. Before leaving town, prepare by turning off your water and setting your thermostat.

How To Manually Drain Your Tankless Water Heater

A manual drain is very simple. It can be needed even if your heater has built-in freeze protection. You should drain your system if you’re going to travel for an extended period of time.

A manual drain valve is easier than draining a tankless water heater without freeze protection.

Freeze protection solenoids are always open and require electricity to keep them closed.

Drain down solenoids automatically open when the power goes out. Higher-end tankless companies include freeze protection devices with their heaters, but you may need to call a specialist plumber to install them.

You must turn off the power supply and cold-water supply before draining the water heater. Make doubly sure to disconnect the electric power before draining the water heater!

You should also ensure that you turn off the gas before you start draining the tankless water heater, if it’s a gas heater. Turning off the gas supply will stop the flow of gas into the heater.

Opening a faucet will release some pressure in the system. Disconnecting the electricity will prevent the heater from heating up.

A bucket should be placed under the water heater to collect the water.

The drain caps must be removed from the isolation valves. Hot water may shoot out of the unit when you open the valves. Be careful when removing the cold water filter.

Remove the cold inlet. You should also remove the drain plug if your water heater has one. It is located at the bottom of the tank.

Built-In Freeze Protection

Higher-end manufacturers and models usually have some type of built-in freeze protection within their units. Their units have ceramic heaters that start operating when the temperature drops below 30 degrees Fahrenheit.

They have a backup heating system if the main heater fails. The sensor triggers the backup system when the temperature drops below freezing. The backup heats up the water until it reaches 58 degrees.

Once the temperature rises above 58 degrees, the backup shuts down.

Such a tankless water heater is well-protected from freezing. If there is no electricity or gas available, manual freeze protection is definitely needed.

Power And Water Supply

Cold water should be turned off before draining the tankless water heater because it could cause damage to the system.

Hot water should be opened up to allow more space for expansion of the pipes. Filters should be removed to prevent clogging.

Turn off the power to the unit, depending on how your system is connected. Unplug the unit if possible, or turn off the circuit breaker (see also our guide on how to match wires size with circuit breaker ). Your tankless water heater (see also ‘How To Keep Your Tankless Water Heater From Freezing‘) should be protected from power surges and outages.

Vent System

Covering vents is important because leaves and other debris get stuck inside. Squirrels also get caught in vents.

How To Return A Tankless To Normal Operation

How To Return A Tankless To Normal Operation

Once the threat of cold weather passes, you should check that all hot water taps and the gas supply is off. You should replace all drain plugs. Water drain plug, pump drain, and condensate drain plug.

Replace the check valve drain plug, replace the cold water inlet, open the cold water supply valve, open a hot water tap, turn off the electrical power, turn on the electrical power, verify that the temperature controller is set to OFF.

How To Thaw A Frozen Tankless Water Heater

If the exterior piping to the water heater freezes, or the water heater freezes, do not operate the unit. Close the gas shut off valve and turn off the electrical power. Allow the tankless water heater (see also ‘Tankless Water Heater Installation Cost‘) to thaw.

Open the water supply valve to see if the unit has thawed. If water flows, then the tankless water heater (see also ‘Gas Vs Electric Tankless Water Heater‘) is thawed.

You should check your gas and water valves before turning on the power supply. If everything looks fine, then you can open them and turn on the electricity.

You should check the gas and power supply before returning the water heater to normal operation.

You should also check the external plumbing for leaks. If you see a leak, call a professional plumber.

Check the internal parts and pipes for any leaks. If everything looks fine then turn on the electric power.

Thawing Pipes After A Freeze

Frozen pipes are located near the main water pipes. Faucets on the same level as the main water pipe freeze first. Faucets on different floors freeze last.

There may be a frozen section of the pipe even if the pipe is still warm in places, but the rest of the pipe is colder than normal. Look for signs of freezing like a bulge, frost, or ice on the pipe.

If there are no signs of freezing, check the temperature of the pipe.

A frozen pipe can cause a burst pipe. When this happens, the water inside the pipe freezes and expands as it gets colder. This causes the pipe to crack and leak.

To fix this problem contact a licensed plumber or property manager.

Wrap towels around the damaged pipe to absorb the leaking water. Then, use a hairdryer to thaw the pipe.

After about 10 minutes or so of thawing with the hairdryer, turn on your faucets (see also our article on letting your faucets drip) to let some water flow.

Open the cold-water faucet closet closest to the frozen pipes to relieve pressure and reduce the chances of breakage.

Grab your hairdryer, and keep on thawing as the trickle of water flows. Your pipes will be thawed in no time!


Cold weather can cause everyone to have worries – and even more so when you consider your water heater! Hopefully, this guide has helped you out!

author avatar
Charlie Hardcastle


On Key

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