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Rinnai tankless hot water - just shuts down after 5-8 minutes

This is a brand-new unit, installed by an authorized technician.

If I run it to draw a bath, I get maybe 1/4 of a bathful, then the system shuts off.

A shower runs out of hot water in 5 minutes.

Trying to wash dishes and run the hot water for a rinse, the system shuts down.

The installer came back and found no issues.

It happens about 80% of the time, but not consistently.

I've looked at the troubleshooting manuals, but don't see this issue. It's not a "sandwich" of cold water. The system just shuts off, and never turns back on again.

Solution is to turn off the water, wait 1 minute, and turn it back on, but this is a *brand new system*


  • Snowmelt
    Snowmelt Member Posts: 1,394
    then if he is authorized dealer and he see the problem he should be able to get a new one
  • lchmb
    lchmb Member Posts: 2,997
    did you check the water strainer for debris? When the unit shut's off, do not shut the water off..Go to it and see if it is flashing a code. If not have him check the impeller to see if it's blocked as well..
    Gordyj a_2rick in Alaska
  • j a_2
    j a_2 Member Posts: 1,801
    The water strainer is on the lower right side of the unit...it's a black knurled quarter sized plug....Often on i seals that were done to replace a failed water heater debris will be in the domestic system....Your ariearors on fixtures will even clog up....Is it sized correctly? Ground water temps are an important variable....Bit surprised your authorized installer is not on this. my need removal to the unauthorized list.....post some pictures....we will know just how authorized he is
  • j a_2
    j a_2 Member Posts: 1,801
    See if it's a code 11
  • Jack
    Jack Member Posts: 1,046
    You don't list the model! Is it a condensing unit. Is it throwing an error code 25? Look in your manual and you can show the error code history. This is a common problem with improperly installed condensate drain lines. The unit is internally trapped and additional traps will fault the unit out. You can check this yourself by disconnecting the drain line below the unit and let the unit drain into a bucket temporarily.
  • FrameMaster
    FrameMaster Member Posts: 2
    Hi Jack, I have the same problem with my RUC90i Rinnai. Just installed a few months ago by a licensed plumber, and I have the same issue. I get a code 25. I just drained the condensate trap drain plug. If it is an improperly installed condensate drain line, how can I correct this? What should I look for that will tell me it is improperly installed?
  • Jack
    Jack Member Posts: 1,046
    Disconnect the drain line at the factory connection at the bottom of the water heater. Run a piece of clear vinyl tubing or pvc to a bucket and let the unit drain into a bucket. Terminate the drain above the lip of the bucket. Report back!
  • j a_2
    j a_2 Member Posts: 1,801
    To the posters....step back and take a picture of the installation..It really helps in resolving issues....list the model number and amount of hot water fixtures it serves.....If in fact the installer is a so called authorized installer,whatever that means....Why can't he fix it...Also ask the installer if he did a gas pipe sizing chart....They are great units, when they are properly sized and installed....Your local rep should offer technical help...if the unit is installed properly....
  • stephenmatlock
    stephenmatlock Member Posts: 3
    Thanks, everyone. Sorry, being Christmas, I got busy. I'll get a picture and let you know. I suspect it is likely the drain line, first, or the water flow, second. I'll also see if the filter is plugged.

    I have the guy coming out in two weeks to review the installation.
  • Jack
    Jack Member Posts: 1,046
    Also, Stephen, get into the manual and learn how to operate the controller. It will tell you a LOT of things about the water heater. It stores error codes, will read flow in tenths of a gpm and many other things. I know you don't want a hobby, or another hobby, but under the circumstances, and informed consumer is best.
  • stephenmatlock
    stephenmatlock Member Posts: 3
    Jack said:

    I know you don't want a hobby, or another hobby...

    I laughed at that.

    I'll get the manual.

    I've already taken the cover off to examine it, so it shouldn't be hard to use the manual to get more understanding.

  • AdamAlvin09
    AdamAlvin09 Member Posts: 2
    I'm also having kind of similar problem and it is frustrating. Did you find any fix? Please share so that I can fix it.
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 2,122
    @AdamAlvin09, welcome to Heating Help. To make sure your question doesn't get buried at the bottom of an old thread, please start a new post. Thanks!