How to Winterize a Tankless Water Heater and Protect the Plumbing System

Rinnai RUR199 tankless water heaterRinnai tankless water heater

If you have a tankless water heater that you are not planning to use for some time and the forecast shows incoming cold weather and freezing temperatures, it is essential to protect the unit and plumbing system.

So, in order to avoid unit failure, use this step-by-step guide and learn how to winterize a tankless water heater properly.

Most of the new tankless water heaters, coming from the manufacturers like Rheem, AO Smith, Rinnai, Noritz, Takagi, Bosch, Paloma, and others, utilize the advanced technology and features for the freeze protection - protecting the system from freezing, down to -30 F, even lower.

However, you, as the owner of a new tankless water heater, should not rely on such features.


Because all the units use electric power, even the protection system (which is usually a heating element or sensor), if there is a power outage, guess what... your tankless unit will fail. Moreover, this is what many people experienced at the end of 2017, during the "arctic" winter.

This is why you should properly winterize a tankless water heater and be ready for the cold days.

Note: Almost every manufacturer of tankless heaters specifies that the heater must not be installed in the area where the temperature can reach 36 F or lower. If the precautions are not taken, like correct draining, the damage to the tankless unit and its components will not be covered under warranty. Adding the anti-freeze solution is also not recommended as it can cause damage to the heater's components.

This is especially important if the tankless water heater is installed in places like cabins, garages, and if you are absent for a long time.

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How to winterize a tankless water heater: Step-by-step guide

One of the main steps when winterizing an unattended tankless heater is to drain and unplug the unit. If there is no water in the heater's pipes, especially in the heat exchanger, the unit will not be damaged due to the freezing conditions.

So, how to prepare the heater for winter?

  • First, you have to turn the electrical power and gas supply OFF. Turn the gas OFF by using the main valve on the gas supply line. For the electricity, unplug the power supply cord or turn the power OFF on the breaker panel. If the unit has the display at the front of the unit, it should be black, with no lights.
  • Keep in mind that there still might be some hot water inside the unit. If the unit was operating and before draining, wait for a while until the hot water cools down.
  • Shut OFF the water supply on the main shut-off valve.
  • Open the taps so the system can drain and release the pressure from the plumbing system.
  • Disconnect the incoming and outgoing water pipes from the tankless heater.
  • Remove the inlet water filter.
  • Use the bucket to collect the residual water. While draining, make sure that it fully drains from the system.

Some manufacturers recommend using the air compressor - to blow short bursts of air through the inlet connection to ensure no water is left inside the heater.

Now the tankless water heater doesn't contain any water, and it is fully winterized.

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