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Rinnai tankless Water Heater not providing hot water

Hi All,

We just moved into new construction house and are having problem with basic hot shower (not filling Tub, etc). We came from Condo world and been living there for past 8 years. Never had a problem with hot water in past 8 years.

Home Info:
-tri level townhouse
- Floor 1 = 1 bd + 1 bath
- Floor 2 = Living+ Kitchen + Powder room
- Floor 3 = 3 bd + 2 bath (one of them is master Bd+ bath)
- We are mostly using floor 1 bathroom right now and kitchen. Have not added furniture to floor#3 yet

However, our new Townhouse is causing us some grief especially with hot water. We have Rinnai RUR199iN model tankless water Heater. Model link below

We have setup Rinnai Control WIFI module and have also setup app for re-circulation.

Out of 50 or so showers we have had, we would have had probably 5 hot showers probably. Is this how Tankless water heater works? Is there problem in our setup or plumbing? do we need to add insulation to metal pipes?

I have not increased temperature from 120->140 yet but I dont think that will fix problem.

what should I try to do next to find a solution to this problem?

here are the pics of the setup


  • niklaw1
    niklaw1 Member Posts: 9
    Is this isolated to just the shower? I would start with adjusting the scald guard on the shower valve.
  • vkdelta
    vkdelta Member Posts: 2
    thanks. I would try it. did not know such a setting existed in shower control.
  • delta T
    delta T Member Posts: 883
    Are you getting cold water or warm water (not warm enough for showering)? Does the unit kick any error codes? as niklaw1 says, is this isolated to just the shower or do you have problems elsewhere in the house?
  • Jellis
    Jellis Member Posts: 228
    If you are getting warm water at the shower then turn that temp up on the heater, try 125 and see how it feels and go from there.
    i have not had very many customers that were satisfied with 120 set at the heater. normally 125 makes them happy, if they have a long run to a fixture then maybe 130.
  • nibs
    nibs Member Posts: 499
    I do not see a pressure relief valve, needed but not the cause of your problem.
    Also if it is a condensing unit, do not see a condensate drain unless it is the PVC pipe that goes vertical on the left, or the longer PVC pipe that goes into the wall below, if not drained properly, will give problems.
    If both of those are there, ignore this post.
  • delta T
    delta T Member Posts: 883
    @nibs relief valve is there teed off the cold inlet. PVC discharge though....
  • SuperTech
    SuperTech Member Posts: 1,940
    > @delta T said:
    > @nibs relief valve is there teed off the cold inlet. PVC discharge though....

    I saw the same thing. At first I thought it was condensate drainage because of the PVC, then I saw the relief valve and just shook my head. Where does the condensate drain go?

    If you are having the same issue with inadequate hot water in every hot water tap in the house I would start with the simple things, check the unit for fault codes and signs of malfunction. If everything is ok then try setting the temperature higher. I would also consider getting the unit descaled and flushed. Is water quality an issue in your area? Are you on a public water supply?
  • Intplm.
    Intplm. Member Posts: 1,468
    niklaw1 said:

    Is this isolated to just the shower? I would start with adjusting the scald guard on the shower valve.

    @niklaw1 is correct. You need to check the faucets in your house. Each faucet separately.
    Make a note of what each faucet or shower valve is doing .
    This is probably just in the shower valve that you have been using.
    If it is only that shower. Post a picture of that one and we will see what we can do.
  • DZoro
    DZoro Member Posts: 1,048
    Hard to tell from the pic, what size is the hard gas pipe? How many BTU's can the yellow flex gas tubing handle? Should state capacity on the yellow tag.
  • Intplm.
    Intplm. Member Posts: 1,468
    That size Rinnai should be 3/4 inch.
  • Slimpickins
    Slimpickins Member Posts: 333
    The best way to troubleshoot the unit is to shut off the hot quick turn ball valve to the house and hook up a hose to the hot drain on service valve and run it. Once you get flow, push and hold down the down arrow on control for 2 seconds, after 2 seconds with the down arrow still down, press the on/off button for a moments and release both. 01 should pop up and then the GPM's, there is no decimal point, then push the up arrow, that is the outlet temperature.
    If temp stays consistent, you have a cross-over somewhere in the plumbing.
    This comes with a recirc pump, I don't see a dedicated return so are they using the thermal by-pass valve that came with it? Also should have a expansion tank if using the recirc.
  • JacquesD23
    JacquesD23 Member Posts: 11
    Unless the 2nd stage regulator is right outside the other side of that wall... Then the gas pipe should be 3/4"... Currently you have half.
  • rick in Alaska
    rick in Alaska Member Posts: 1,429
    Like the others have said, check and see if you get hot water out of the bathroom sink, or another sink. If you do, then it could be the shower valve just needs an adjustment. There is also a possibility the inlet filter has some debris in it from the installation and needs to be flushed.

    The drain for the relief valve is cpvc, not pvc, and is ok for it. I can't tell by the picture, but it looks like the gas pipe is the same size as the inlet fitting, which makes me think it is 3/4, which is fine.
  • hcpatel78
    hcpatel78 Member Posts: 150
    edited March 2020

    There is DIP switch setting for some initial setup. Please check the manual in detail. I have a similar heater installed myself in 2018 and have to remove all scold guards from both showers in my house. Measure the temperature with a simple thermometer. We used to live in an apartment where they have baseboard heat and hot water source was common, so they have cranked up DHW temp so much when we start to use 120 F hot water at our new house out of tankless our family felt that water temp.is cold.
    Thank you,
    Hiren Patel