Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit

Rinnai Tankless Water Heater Will Not Flush

deblaw10 Member Posts: 5
I have owned a Rinnai Tankless water heater for over 10 years. I flush the unit quarterly with vinegar. I have tried to flush the unit several times over the past few weeks and have been unsuccessful. The pump is working, but the unit is acting like the valves are closed. I have never experienced this before.

I spoke with Rinnai and they told me my transfer pump was too powerful. The one I was using was transfering at 25 gallons per minute. I needed one that pumped 3-5 gallons per minute. I found a garden pump and tried, I was unsuccessful. Called Rinnai again and they said my pump isn't powerful enough. I asked for a recommendation for a pump, they do not give recommendations. I went back to my old pump and attempted to pump the unit again with Rinnai suggesting to turn my hot water on and shut the water off from the tank instead of the faucet. This will keep the valve open. This was also unsuccessful. Any ideas why the unit is not flushing?


  • nibs
    nibs Member Posts: 462
    No suggestions about why, but if you can get your hands on a 12V RV water pump (Around $40 new), try using it they put out about 3gpm at up to 40 psi. If you were near, I would give or lend a used one that you could use.
  • deblaw10
    deblaw10 Member Posts: 5

    Thank you! I did purchase a 3gpm pump, but I was told by Rinnai after I purchased that it needs 18foot head. Those are hard to come by this time of year. I don't understand why the pump type I have been using for the past 11 years suddenly doesn't work.
  • Leon82
    Leon82 Member Posts: 684
    Could the impeller be worn?
  • deblaw10
    deblaw10 Member Posts: 5

    I have tried 3 different pumps, all work fine until they are hooked up to the water heater. It's like the valve is closed, but it isn't.
  • Leon82
    Leon82 Member Posts: 684
    Inlet screen clogged?
  • deblaw10
    deblaw10 Member Posts: 5

    No, the inlet screen is clear of debris.
  • Larry Weingarten
    Larry Weingarten Member Posts: 2,089
    Hello, A trick I've used to unclog plumbing is to reverse flow, repeatedly. That way if there is sediment plugging things up, it will eventually get worked loose. I don't know if you have a check valve in there someplace; if so this idea wouldn't work. Still it seems it couldn't hurt to try.

    Yours, Larry
  • deblaw10
    deblaw10 Member Posts: 5

    I have tried to reverse the flow, but no luck, however, I did not try several times. I have never had this problem before, like I said, I flush my unit quarterly due to having very hard water.
  • bobn4907
    bobn4907 Member Posts: 1
    so how did you resolve your issue; I believe I have the same problem
  • Dekito
    Dekito Member Posts: 1
    I have rhe same problem ,done many times now its not working 
    Le John
  • Intplm.
    Intplm. Member Posts: 1,283
    Has anyone called Rinnai customer tech support?
    What did they suggest doing?
Sign In or Register to comment.


It looks like you're new here. If you want to get involved, click one of these buttons!