You had a big cold snap and the power went down, your outdoor tankless water heater wasn’t able to go into freeze protection mode and is now more ice than water. When this occurs, it’s crucial to address the issue promptly to avoid as much damage and disruption to your water supply as possible. Operating the unit in a frozen state is not advisable. If you find yourself facing a frozen Rinnai tankless water heater,you can thaw it out and restore functionality as long as it didnt freeze to hard.

Here is how to unfreeze it and restore to normal function

  1. Close the gas and water shutoff valves serving the water heater to prevent any further damage.
  2. Turn off the circuit breaker that powers the heater to protect both you and the internal electronics.
  3. Allow the system some time to thaw naturally. If the unit is outdoors which is most often the case with this issue your going to need to set up a small tent around the unit and a space heater to bring the ambient temperature up above freezing and give everything an opportunity to thaw out
  4. Once thawed, open the water supply valve and check if water is flowing through the unit.
  5. Examine the tankless water heater, its internal components, plumbing connections, and external pipes for any signs of leaks or damage. This is very likely to have happened especially in the heat exchanger manifold due to it being thin copper.
  6. If water is flowing normally and there are no leaks, you can proceed to open the valves and turn the electricity back on to resume operation.

It is crucial to contact a plumber if you notice any leaks in the water heater or the pipes connected to it. Attempting to fix the unit yourself can lead to further complications and may not address the root cause of the problem effectively.

After you are done thawing it out you might need to do a reset see: How to reset a rinnai tankless water heater.

Preventing Freezing in Rinnai Tankless Water Heaters

To avoid freezing issues with your Rinnai tankless water heater, you can employ two preventive measures: draining the water heater or setting the water to a low flow.

  1. Draining a Tankless Water Heater: If your Rinnai tankless water heater does not have built-in freeze protection, you can drain it as a precautionary measure before an anticipated cold spell or when you’ll be away for an extended period. Here’s how:
  • Turn off the cold water and gas supply, as well as the temperature control and electrical power.
  • Open a hot water tap to relieve any pressure.
  • Place a bucket under the unit to catch the released hot water.
  • Remove the drain caps on the hot and cold isolation valves to allow the hot water to drain into the bucket.
  • Proceed by removing the cold-water inlet filter and then the drain plugs at the bottom of the heater to ensure complete drainage.
  1. Running a Low Water Flow: In situations where the temperature drops significantly, causing your tankless water heater to struggle with freezing, reducing the water flow can help prevent freezing. This approach is also useful during power outages. Follow these steps:
  • Turn off the power to the heater and close the gas supply valve.
  • Open a hot water faucet to create a small, steady flow of water. You should observe a flow rate of approximately 1/10th of a gallon per minute, with the water stream not exceeding 0.20 inches in width.
  • By reducing the water flow, you minimize the amount of water left in the plumbing system, reducing the risk of freezing.

Winterizing a Rinnai Tankless Water Heater

If you plan to be away for the entire winter season, you can take additional steps to winterize your Rinnai tankless water heater effectively:

  • Turn off the gas, water, and power supply to the unit.
  • Start by shutting off the cold-water supply and draining the unit by opening the solenoid valves on both the cold and hot water lines. Open some hot water faucets to facilitate drainage.
  • Remove the inlet filter on the cold-water line to allow for expansion in case of freezing.
  • If accessible, cover the intake and exhaust vents of the venting system to prevent debris or animals from obstructing airflow.
  • Insulating your pipes is another essential protective measure. Consider using pipe insulators that come with a pipe heating cable and thermostat, providing heat when needed the most.

Do Rinnai Water Heaters Have Built-In Freeze Protection?

Most Rinnai tankless water heater models come equipped with ceramic heaters specifically designed to protect against freezing. These heaters automatically activate when the temperature drops to a certain level. Additionally, sensors can detect freezing conditions and engage the unit to prevent freezing by turning it on and off as needed. Freeze protection solenoid valves, also known as drain-down solenoid valves, can automatically open to drain the heater when a power loss occurs. Although more common in higher-end models, you may be able to add these valves to your unit for enhanced freeze protection.

By following these guidelines, you can effectively address a frozen Rinnai tankless water heater, prevent freezing issues, and ensure your system operates smoothly even in cold weather conditions. If you have any concerns or require assistance, it’s always advisable to consult a professional plumber with expertise in Rinnai tankless water heaters.