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.

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.

  • Even indoor models can experience cold weather complications!

​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 2 lines of defense within their units.

  1. Rinnai's units have ceramic heaters located on the heat exchanger, water lines and other internal parts. These heaters will begin to work when the temperature drops down into the low 30's.
  2. If the temperature drops too fast, or for any reason the ceramic heaters don't 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 and 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 is no longer a threat of freezing. 

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 (see below). 

Damages Caused by Cold Weather 

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.

How to Thaw a Frozen Water Heater

  2. Turn off the electrical power and close the gas and water shutoff valves. 
  3. Wait for the tankless unit to thaw. Open the water supply valve. If water flows from the valve, the unit has thawed.
  4. Check the external plumbing and internal parts and pipes for leaks.
  5. If you spot a leak, you should contact a professional plumber.
  6. If everything looks fine, open the gas water valves and turn on the electrical power. 

Preventative Steps to Protect your System

A simple and inexpensive way to protect your tankless water heater's external plumbing and valves is to insulate the external pipes. 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 products are available on Amazon and offer added protection as well as saving you from a massive problem.

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:

  1. Turn off the gas supply and cold water supply. 
  2. Turn off the temperature control.
  3. Disconnect the electrical power.
  4. Place an empty buck under the water heater.
  5. On the hot and cold isolation valves, remove the drain caps.
  6. 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).
  7. Remove the cold water inlet filter and any drain plugs on the bottom of the unit. 
Watch The Video

How to Return a Tankless to Normal Operation

  1. Check that all hot water taps are closed and the gas supply is off.
  2. Replace all drain plugs. (Water drain plug, pump drain plug, and condensate trap drain plug).
  3. Replace the check valve drain plug.
  4. Replace the cold water inlet filter.
  5. Open the cold water supply valve and allow the unit to fill with water.
  6. Open a hot water tap to verify that water is flowing thru the unit. Then close the tap.
  7. Turn on the electrical power.
  8. Verify that the temperature controller is in the off position.
  9. Turn on the gas supply.
  10. Turn on the temperature controller.

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.

  1. Turn off the electrical power.
  2. Close the gas supply valve.
  3. 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).

How to Winterize Your Tankless System

Winterizing your tankless water heater is an excellent precautionary measure particularly if you will 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 on 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 is 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.
  • Should there be 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 an issue when it's time to restart your tankless. 
  • You may want to consider hiring a plumber to winterize your unit for you. Verify that he'll guarantee his work and cover any expenses if things weren't properly done. As an added bonus, you can take good notes and do the job yourself next year with confidence!