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

Exhaust Smell from all faucets and showerheads : Tankless Water heater Rinnai RU119iN reu-n3237ff-us

I have a Rinnai RU119iN reu-n3237ff-us Tankless water heater in a new build home completed July 2023.

From the beginning I've noticed an odd smell only when the hot water is used. Especially when running hot water for a shower you can really notice the smell.

The smell predominantly occurs when the system has not been used for a few hours.

The smell is closest characterized to what you smell after lighting a gas fireplace/stove or even exhaust from a vehicle. It is not a sulfur smell, but more like a burnt smell.

There's no smell when the cold water is on and also no smell for microwaved or boiled cold water.

Plumber contracted by the builder used a combustible gas meter to test for gas leaks which had no leaks detected, but then used the same meter for the hot water which triggered the unit and heated cold water also triggered the unit. Later on after research I found that steam can also trigger the combustible meter to give false readings.

Before finding out about false readings I went down the path of instant testing the water for chlorine/hardness/etc as well as getting the water company involved to send cold water samples to a lab for volatile contaminants. The result was nothing detected with respect to the volatile elements. I also reached out to a local water filtration sales rep who did the same quick tests and said a system would not solve the smell issue.

I understand that a tankless water heater is comprised of two separate systems of a pipe passing through heat and there should be no way exhaust can enter the water flow however it is evident somehow its happening.

I've contacted local companies but no one has been able to solve the issue let alone ever heard of it.

For the physical unit there are no error codes and no leaks detected outside the unit. It has not been opened.

Has anyone heard of this sort of issue and possible have a fix for it?


  • mattmia2
    mattmia2 Member Posts: 9,660
    My guess would be it is bacteria and minerals in the water like the sulfur smell, possibly some reaction with the metals too.
    Mad Dog_2Zman
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
    edited March 1
    Passing through the unit the water is quickly heated ... Breaks down the water going through it . Coming out of solution thing...... The unit has been used . My thoughts the water..

    There was an error rendering this rich post.

  • pedmec
    pedmec Member Posts: 975
    Much like descaling the unit run a sanitizer thru the water side of the heat exchanger. there is no chance that flue gases are getting absorbed into the water! Did you ask a plumber to reach out to Navien? you never know what they might have done. Heat exchangers might be being made differently. could be oils in the heat exchanger from manufacturing. i don't know. just spit-balling.
    rick in Alaska
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,301
    Hi, Just to help rule things out, how about turning the heater off and then running water from the hot side? See if there is any odor. If not, you can eliminate the possibility of some other part of the hot side being at fault.
    Is the odor at all hot taps? If not, it could have something to do with drainage not working right.
    Have you had a look at the heater's inlet screen? Any plastic bits there? It's a long shot, but if some plastic bits were in the heat exchanger, maybe heating could create the odor??
    I've dealt with a lot of hot water odor problems, but this one is new to me. :/
    Yours, Larry
    PC7060mattmia2Mad Dog_2Miata
  • PRR
    PRR Member Posts: 141
    We got a 'scorched' smell when hot water ran. New-To-Us on-demand heater fed from a small propane tank. Plumber pointed out that the tank was nearly out, the gas pressure musta fallen every time the big fire came on to heat water. Lean fire probably burned bad. Why it smelled 'scorched' I don't know, but topping off the propane was the cure. The smell was not just in-shower but pretty much the whole house, the un-blown heater's fumes just rose by convection and, if under-heated, had places to slip out of smokepipes and out of cellar.

    Obviously if you are on city-gas, this should not happen (worn/bunged regulator?).
    Mad Dog_2
  • pedmec
    pedmec Member Posts: 975
    That is concerning. i hope all the joints that were leaking in the house are sealed up! having flues gases in the house is a good way of accidental death.
  • rick in Alaska
    rick in Alaska Member Posts: 1,457
    That is also what I am wondering. How is the unit vented? Is there a chance the exhaust is getting back in to the house? If you could show us some pictures of the exhaust, it might help. The last Navien I worked on had a light amount of raw exhaust gas smell coming out the exhaust, and the manufacturer didn't seem to be concerned.
    The heater can no way allow exhaust in to the water, so that is out. Like pedmec said, try running a cleaner through the heat exchanger and see if that helps.