How to Prevent A Frozen Tankless Water Heater

    Cold Weather

    Cold weather can be a problem for tankless water heaters. They often require additional attention in order to prevent them from experiencing weather related problems such as freezing. This is a problem rarely seen in traditional tank-style water heaters but one you can avoid with regular water heater maintenance.

    Most manufacturers don't cover damage caused by freezing under their warranties, so it's important to give your tankless a little extra care during cold weather. You should always check your owners manual for details regarding your specific unit as recommendations vary between manufacturers.

    Protecting Your Tankless From Cold Weather


    Homeowners often worry about outdoor tankless water heaters when it comes to cold weather, but it's important to keep an eye on indoor models as well. Because even indoor tankless water heaters can experience cold weather complications!

    >> Click Here to Learn Other Preventative Tasks <<

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    How to Protect your Tankless from Freezing

    A simple and inexpensive way to protect your tankless water heater's external plumbing and valves is to insulate the external pipes with a pipe heating cable and then add pipe insulation. 


    There are a variety of different products available. Some even have a built-in thermostat designed to heat the pipes when temperatures fall near freezing. These pipe heating cables are inexpensive and can offer you added protection from a massive problem.

    M-D Building Products 4325 M-D 0 Pipe Heating Cable, 6 Ft L

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    How to Run Water to Prevent Freezing

    There are times when setting your tankless to flow a low volume of water thru the unit makes sense. Although, we do not recommend using this method in situations where it would be used for extended periods of time, such as a vacation. It can be helpful if there is a loss of power and the temperature is beyond the unit's ability to freeze protect itself.

    • Turn OFF the electrical power.
    • CLOSE the gas supply valve.
    • OPEN a hot water tap within your house. Set the tap to flow at a rate of 1/10th of a gallon per minute (or the water stream width should be .2 inches).

    Built-in Freeze Protection

    Higher-end manufacturers and models often have some type of built-in freeze protection within their units. Rinnai is a good example of this, they've built-in 2 lines of defense into their units.

    • Rinnai's units have ceramic heaters located on the heat exchanger, water lines and other internal parts. These heaters will begin to operate when the temperature drops down into the low 30's.
    • If the temperature drops too fast, or for any reason the ceramic heaters fail to fire-up, Rinnai has a back-up system installed. A sensor within the unit will trigger when the internal temperature of the tankless falls below freezing. It will then automatically cycle the unit on for several seconds. When the water inside the unit is heated to about 58 degrees, the system will cycle off and on until there's no longer a threat of freeziing.

    Provided there is electricity and gas available, the Rinnai tankless system is well protected from the threat of freezing. If electricity and gas is not available, manual freeze protection should be used.

    Three snow flakes on a blue background

    How to Winterize Your Tankless

    Winterizing your tankless water heater is an excellent precautionary measure, particularly if you'll be away during the winter. Weather can change rapidly and unexpected ice, snow and freezing storms can be especially worrisome if you are not nearby to take the proper precautions. 

    Always check your owners manual for detailed directions for your specific water heater. These instructions are provided as a general guide. Your unit may have different requirements.

    Gas Supply

    • Turn OFF the gas to the tankless water heater.

    Water Supply

    • Turn OFF the cold water supply to the tankless water heater.
    • DRAIN the unit by opening the drain down (freeze protection) solenoid valves on the cold and hot water lines.
    • OPEN several hot water taps within the house.
    • REMOVE the inlet filter on the cold water line.
    • REMOVE the plug or inline filter on the hot water side to leave room for expansion if there's any water left in the lines that freeze. (Not all systems are designed with these fittings on the hot water line).

    Electric Supply

    • Turn OFF the power to the unit. Depending on how your system is wired, you can either unplug the unit or flip off the circuit breaker.
    • If there are any power surges or outages, your tankless will be protected.

    Vent System

    • Place a cover on the end of the intake and exhaust vent if you can reach them safely.
    • Leaves and debris (sometimes even squirrels) enter the vent and become trapped. Air flow issues can be a problem when its time to restart your tankless.

    You may want to consider hiring a plumber to winterize your tankless unit for you. Be sure to verify that he'll guarantee his work and cover any expenses if things aren't properly completed. As an added bonus, you can take good notes and do the job yourself next year with confidence!


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    Draining a Tankless Water Heater

    Draining a tankless water heater is sometimes necessary, even when a unit has built-in freeze protection. If you lose power or plan on traveling for an extended time, it's a good idea to drain your unit, particularly if you live in a cold weather climate. 

    These systems can be drained manually, as we'll cover later, but it is a much simpler task if freeze protection solenoid valves are installed. Some higher-end tankless manufacturers often include these, or your plumber may have had the foresight to add them during installation. 

    If your unit does not have these valves, we highly recommend adding them. They will give you peace of mind during cold weather as they will automatically drain your tankless in the event of a power outage. 

    Freeze protection solenoid valves are also called drain down solenoid valves. They are always "open" and require an electrical current to keep the valve closed. When the power is interrupted, the valve opens and drains the unit.


    How to Manually Drain a Tankless

    If your tankless system doesn't have freeze protection solenoids installed you'll need to manually drain your unit. Manually draining is not as easy, but it's just as effective. Here's what to do:

    • Turn OFF the gas supply and cold water supply.
    • Turn OFF the temperature control.
    • DISCONNECT the electrical power.
    • Place an empty bucket under the water heater.
    • On the hot and cold isolation valves, REMOVE the drain caps.
    • OPEN the hot and cold isolation valves. Use caution, the hot water released will be under pressure. (If you open a hot water tap before you open the valves it will help relieve the water pressure).
    • REMOVE the cold water inlet filter and any drain plugs on the bottom of the unit.

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    How to Return a Tankless to Normal Operation

    Once the threat of cold weather has passed, its time to get your tankless water heater back into service by following these steps:

    • Check that all hot water taps are CLOSED and the gas supply is OFF.
    • REPLACE all drain plugs. (Water drain plug, pump drain plug, and condensate trap drain plug).
    • REPLACE the check valve drain plug.
    • REPLACE the cold water inlet filter.
    • OPEN the cold water supply valve and allow the unit to fill with water.
    • OPEN a hot water tap to verify that water is flowing thru the unit. Then CLOSE the tap.
    • Turn ON the electrical power.
    • Verify that the temperature controller is in the OFF position.
    • Turn ON the gas supply.
    • Turn ON the temperature controller.
    Three ice cubes melting

    How to Thaw a Frozen Water Heater

    Cold weather will not only cause the plumbing leading to and from your tankless to freeze, it can also create havoc as the internal parts within the unit can freeze as well.

    Steps to Thaw a Frozen Water Heater

    • DO NOT OPERATE THE WATER HEATER.
    • Turn OFF the electrical power and CLOSE the gas and water shutoff valves.
    • Wait for the tankless unit to thaw. OPEN the water supply valve. If water flows from the valve, the unit has thawed.
    • Check the external plumbing and internal parts and pipes for leaks.
    • If you spot a leak, you should contact a professional plumber.
    • If everything looks fine, OPEN the gas water valves and turn ON the electrical power.

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