Tankless water heater - Rinnai or Navien or ???

I have a ten year old Rinnai tankless heater that is still heating great but it seems to have stopped burning all the fuel. It's basically farting gas into the closet and i need to get that stopped.

I'm not inclined to throw the parts cannon at a ten year old heater. 

What says the hive about best natural gas indoor tankless heaters in 2025?

(Also pretty disappointed that it only lasted ten years but it is what it is - if you zoom into the photo you can see the dates that I flushed the heater and cleaned out the filter or the vent and fan)

have navien in few properties. Oldest is 14 years

I do service every 24 months

no issues at all 

all 3 of mine are outdoor on side of house 

We bought our house in 2020, and the seller's disclosure sheet mentioned 'Rinnai Tankless water heater is acting up and will likely need replacement in the near future'.  I figured it was a lost cause, so I've never actually done anything to it, simply waiting for it to die as it was supposed to.  Fast forward to 2025, with literally ZERO maintenance/blowdowns/flushes/anything, and she's still chugging along like a damn champion. 

And for that, my vote is Rinnai, haha. 

i have a Navien.  One thing to consider, the Navien warranty is only valid if it's installed by a certified Navien professional.  

the problem with that is that Navien installers all want to charge a fixed fee for install and that fee is based on a roughly 2.5 day install time.  I called several of them asking if i could pay rack rate labor and retail for the unit and was given the run around.  

that being said several plumbers did claim that they have the ability to fix/support/repair tankless hot water heaters which is likely a much cheaper way than replacing the entire unit.  so unless you're willing to replace it yourself and give up the warranty, maybe start with asking if a plumber / HVAC technician can service/repair your existing unit.  

I have sprayed down all the piping with soapy water and found no bubbles so the leak is internal. Parts cannon could be a solution but it's already 10 years old... 

The plumber that installed it is gone but another who was recommended will come and look at it tomorrow. 

I did have a "Rinnai Pro" tech (of the variety with 250 trucks around the city) come see it and he quoted around $7k "and could do the job today" for replacement. And $3-4k to swap some parts that wouldn't have a warranty. A new Rinnai heater of the same size costs $1,400 so I decided that was a lot excessive. 

OHSCrifle said:

I have sprayed down all the piping with soapy water and found no bubbles so the leak is internal. Parts cannon could be a solution but it's already 10 years old... 

The plumber that installed it is gone but another who was recommended will come and look at it tomorrow. 

I did have a "Rinnai Pro" tech (of the variety with 250 trucks around the city) come see it and he quoted around $7k "and could do the job today" for replacement. And $3-4k to swap some parts that wouldn't have a warranty. A new Rinnai heater of the same size costs $1,400 so I decided that was a lot excessive. 

this is the same problem i had when my bosch died... every plumber wanted to charge me the "fixed fee" replacement which is built on replacing a tank based water heater.  $7k for a unit with a retail price of 1/3rd of that is excessive.  While I understand the concept of value based pricing, they were effectively charging me full retail for the unit plus 2.5 days of labor for something you can buy online or at a hardware store for usually 80% of retail.  

ClearWaterMS said:

OHSCrifle said:

I have sprayed down all the piping with soapy water and found no bubbles so the leak is internal. Parts cannon could be a solution but it's already 10 years old... 

The plumber that installed it is gone but another who was recommended will come and look at it tomorrow. 

I did have a "Rinnai Pro" tech (of the variety with 250 trucks around the city) come see it and he quoted around $7k "and could do the job today" for replacement. And $3-4k to swap some parts that wouldn't have a warranty. A new Rinnai heater of the same size costs $1,400 so I decided that was a lot excessive. 

this is the same problem i had when my bosch died... every plumber wanted to charge me the "fixed fee" replacement which is built on replacing a tank based water heater.  $7k for a unit with a retail price of 1/3rd of that is excessive.  While I understand the concept of value based pricing, they were effectively charging me full retail for the unit plus 2.5 days of labor for something you can buy online or at a hardware store for usually 80% of retail.  

I just might replace it myself if the warranty is that lousy. 

What about just cleaning up the burner fixture? 

That said, I installed a propane Rinnai last year on a new install and it is working well. It is not hard.

I have a Rinnai.  It's... 20 years old?  It's had almost zero maintenance and it still makes as much hot water as I need, as soon as I need it.

low_n_slow said:

What about just cleaning up the burner fixture? 

That said, I installed a propane Rinnai last year on a new install and it is working well. It is not hard.

Not sure how that would be done. I did contact Rinnai last night and was advised a new model has the exact same EVERYTHING as far as water, gas and exhaust connection placement. 

Take a look at this installation / maintenance manual, I'm not sure if it applies to your specific model or not.  They mention an inlet air filter, if yours has one and it's dirty or restricted it may be causing the unit to run rich / poor combustion that could result in a gas smell.  Make sure the outside air inlet pipe and the vent pipe are both clear of any blockages too.

https://images.salsify.com/image/upload/s--pdKkmXZb--/ycbfmbyhllwrlmre5ouw.pdf

Navien here for 11 years. Very easy unit to work on when/if you need to. Over the years I've needed to replace a few small items, all available online and at my door in a day or two. I've also done a bunch of research and picked up a few parts/pieces that the interwebs says go over time. I keep them on a shelf and have replaced as needed. A few o-rings on-hand make most small leaks go away quickly. 
 

Once every year or two I de-scale the unit, but honestly there has never been anything in the bucket afterwards, I just do it because we're on a deep well and it was highly suggested. 
 

When both my parents and brother need a new HWH in their houses, they both went Navien and couldn't be happier. 
 

Since ours has been so reliable, if it ever "dies", I would buy another one and install it myself. The warranty wouldn't be a concern based on the purchase/parts pricing vs "authorized installation" and service calls.
 

I'd gladly roll the dice and DIY the next one.

11GTCS said:

Take a look at this installation / maintenance manual, I'm not sure if it applies to your specific model or not.  They mention an inlet air filter, if yours has one and it's dirty or restricted it may be causing the unit to run rich / poor combustion that could result in a gas smell.  Make sure the outside air inlet pipe and the vent pipe are both clear of any blockages too.

https://images.salsify.com/image/upload/s--pdKkmXZb--/ycbfmbyhllwrlmre5ouw.pdf

That's a good tip. I have cleaned it out several times but may need to increase the frequency. 

I have a Navien I like it, though I have only had it since October 2024.  My neighbor, a retired HVAC guy installed it.

I'm kinda surprised there isn't "Mr. Cool" for tankless water heaters. A retailers that skips the middle men, brands their own stuff, sells direct, and has lots of documentation and support to assist in install. 

Duke said:

I have a Rinnai.  It's... 20 years old?  It's had almost zero maintenance and it still makes as much hot water as I need, as soon as I need it.

 

My instructions that came with my ot water heater says it should be inspected/serviced every two years.  I'm not saying that yours is not OK, but maybe get it looked at?

Cheers!

Rinnai confirmed the chassis is unchanged so everything is an easy hook-up. 

Had a plumber visit today who will swap in a new Rinnai for $500 labor. He said it would only take a couple hours. He also said the gas smell is super faint and a lot of the gas equipment he works on smells no different. He did agree it could be burning lean due to partially blocked air path. He suggested if it's still heating the water - let it eat.

So I'm pretty likely gonna replace in-kind.. AFTER I vacuum out the airway again and see if that settles anything down. 

All the discussion is appreciated.