How do I fix my Rinnai code 12?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

If you have a Rinnai tankless water heater, Code 12 is an error code that indicates that the water temperature inside the unit is too high. This can happen for a number of reasons, such as the water heater being set too high, a build-up of scale inside the unit, or a malfunctioning thermostat. If you see this error code, it's important to call a plumber or Rinnai customer service to have the unit checked out and repaired.

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1. Check the gas line for leaks

The steps to check the gas line for leaks in order to fix rinnai code 12 are as follows:

  1. Turn off the main gas supply to the house.
  2. Open all windows and doors to allow the gas to escape.
  3. Check the gas meter. If the meter shows that there is no gas remaining in the line, then the leak is most likely in the line itself.
  4. If the gas meter shows that there is still gas in the line, then check for leaks by following these steps: a. Look for any areas where the gas pipe has been punctured. b. Look for any areas where the gas pipe is rusting. c. Look for any areas where the gas pipe is sticky.
  5. If any of the above leaks are found, then Fix rinnai code 12 by repairing or replacing the gas line as necessary.

2. Check the igniter for dirt or debris

  1. With the rinnai code 12 still turned on, open the damper on the top of the unit.
  2. With a flashlight, look for dirt or debris on the igniter. If there is any, use a can of compressed air to clean it off.
  3. Close the damper and turn off the rinnai code 12.
  4. Reinstall the igniter cover.

3. Clean the burner assembly

  1. Disconnect the gas line from the burner assembly
  2. Remove the burner assembly from the refrigerator
  3. Clean the burner assembly using a stiff brush and hot water
  4. Reinstall the burner assembly into the refrigerator

If you didn't find success with an option above, then try:

  1. Check the thermocouple for proper operation.
  2. Replace the thermocouple.
  3. Check the gas pressure.
  4. Adjust the gas pressure.
  5. Call a professional.