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rinnai RL75i code 10

Our Rinnai RL75i water heater has been giving us a code 10 after 8 years of flawless operation. I have flushed the heat exchanger, cleaned the fan and cleaned the burner with the help of an excellent Rinnai service tech. The exhaust and air intake are clean and unobstructed. The tech thoroughly checked the unit and said everything looked ok. We are still getting the code 10, usually from running bath water in the upstairs bathroom. If we turn off the water and turn it back on everything is fine although occasionally we have to do this a second time and rarely a third time. The tech said if the code 10 continues the next step would be a more complicated check of the electronics. Can anyone give me any ideas on what to do next?


  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,355
    edited December 2019
    Code 10 is a "blocked vent" code. The indications are that your air intake or exhaust may have some restriction. This is measured by an air pressure sensor. You may have a blocked vent, remove the blockage. You may have a build up of dirt on the fan that provides combustion air, Clean the fan. you may have a defective sensor, replace the sensor

    The code indicates the approximate cause of the fault, and gives a direction to start looking. Most problems with Tankless water heaters are low gas pressure or blockage in the water side of the heat exchanger due to build up of minerals. Code 10 does not point in that direction. Look at the path the air for combustion takes to get in, and the path the byproducts of combustion takes to get out.

    There are 2 sides to the heat exchanger, the fire side and the water side. Looks like you have been diligent with the water side. Have you checked the fire side where the hot exhaust gasses go to transfer the heat to the water?
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16
  • srhfb
    srhfb Member Posts: 3
    Thanks for your reply. We have removed and cleaned the burner. This was done with the assistance of a certified rinnai service tech. I would assume he checked the exhaust when we removed and cleaned the burner.
  • srhfb
    srhfb Member Posts: 3
    What sensor do you mean and where is it located?