Navien tankless heater releases excessive unburned gas during every start up.

svuk15

We had a Navien NPE-240S (nat gas) tankless water heater installed about one year ago and continue to smell unburned gas in our backyard coming from the exhaust vent of this unit. I would like to tell our story in hopes of getting some feedback from people experienced with tankless water heaters and possibly give a warning to people thinking of using a tankless water heater - specifically a Navien unit.

The long story...within weeks of the Navien install we smelled gas coming from the exhaust vent and error code E003. Roughly 1-2 per week we didn’t have hot water so I would look at the unit and see E003 error code. Resetting the unit would get the hot water working again. Told our general contractor and plumber who installed the unit about the problem and was told the unburned gas was coming from our main natural gas regulator on the side of the house. Clearly getting the run-around from these folks but was willing to undertake the journey to hopefully get things fixed. After more back and forth I called the natural gas utility to come check the gas smell. They used a gas detector to confirm it was coming from the tankless water heater and they also measured high CO from the exhaust.

From there our contractor and installer contacted Navien and the supplier to get support. It took a couple months and multiple tries but eventually Navien sent a “rep” to look at the unit. He was honest in admitting he was only a sales rep but he had some tools to do basic testing. He contacted NAvien phone support and the installer was there too. They did not have a combustion analyzer but through the Navien phone support they checked a few things and made some minor adjustments to the gas valve settings. I was skeptical but they thought there was a good chance this would fix the gas smell and the error code. When I asked more questions about the gas smell the Navien rep said a couple interesting things: I should try running the exhaust vent up the house to vent above the roof; and ff I wasn’t satisfied with the smell of unburned gas in our yard then maybe a tankless heater was not suitable for me.

The problems remained. Still smelling unburned gas and E003 error code. Another month or two of phone calls and Navien finally sent a real technician to troubleshoot. The fix for the E003 was painfully simple. The control unit was set for the wrong elevation. A few dip switch changes and this was fixed. The error code has not appeared since. The technician also attached the combustion analyzer and adjusted settings to be in the middle of CO and excess O2 acceptable ranges. So good news however the smell of unburned gas remains - I think it improved after the technician adjustments but the whole family can still smell gas about 30 ft away from the exhaust vent when the unit starts up.

At this point we are essentially giving up. Our contractor did an overall good job on our house reno. Customer support from Navien is horrible - they will give you the run around and suggest ridiculous fixes like venting through the roof.

So do we have a bum unit or is this typical for a tankless heater or specifically Navien heaters?

Leon82

My Bosch does it. It is purging as it injects gas and fires so there will always be some that comes out

Repeated short cycles will make more of a smell.

EBEBRATT-Ed

I guess there are 4 questions:

Is it unburned raw natural gas or exhaust fumes you are smelling?

Why is the heated exhaust fumes staying low to the ground and not rising to where they would not be objectional?

Do you smell raw natural gas on start up ? Are the flue gas fumes rising up and not objectional while the flame is on?

Could the exhaust flue be relocated?

How a bout a few pictures of the exhaust coming out of the house

STEVEusaPA

How many months from first complaint until now?

svuk15

Thanks for the replies. It's somewhat comforting to know other units vent some unburned gas during purge. Answer to questions:
- definitely unburned natural gas when unit first fires up. after a few seconds the smell is combusted gas and not objectionable. The utility tech measured 10% LEL right at the exhaust vent.
- it would be challenging to relocate exhaust vent further away from backyard. extending exhaust vent up the side of house would look strange. Photo attached. The middle white vent is tankless heater vent. The far white vent is furnace exhaust. Black vent is air intake for tankless heater.
- It took 5 months since first complaint to partial resolution. It is now 1 year since first complaint but I haven't been actively trying to resolve the problem.
-

Jellis

My first thought is get rid of those Tee's, raise the exhaust above the fence line and use 45°s to project the exhaust away from the house and fenced in walkway.
I would expect that fenced in area to create a zone where exhaust gas' may be trapped and not freely escape to the open air.

EBEBRATT-Ed

Agree with @Jellis above.

@svuk15 3 other options to think about. Run them up the outside of the house and cover them with "line hide " if you can find some large enough or box them in and cover the box with siding.

Do you have a closet you can rum up through and vent through the roof?

kcopp

At least try to get the vents up a couple feet , less the tees. If that helps you are on to something.

KeenGreen

Just a thought.....What about the distance of the gas regulator to the Navien unit itself? if the reg is within 6' it may be getting a build up of gas pressure in the combustion chamber. When the unit purges before firing it may be releasing the fuel from the combustion chamber to the outside?

Jeff

svuk15

The gas regulator is about 20 ft from unit. The technician checked fuel supply pressure during different loads and it was in spec.

svuk15

Raising the vent a few feet would be fairly simple and I can imagine it would help somewhat. Over the past year I have been looking at other house vents in our neighborhood and I haven't seen an elevated vent as described.

I still have the same fundamental question. Is something wrong with my particular unit or something with the Navien design?

I understand the reason for a purge of the combustion chamber prior to firing but I don't understand why in normal operation a unit would purge unburned gas every cycle.

mattmia2

I don't think it would be unusual to release a small amount of unburnt gas when it first fires as it is lighting. It doesn't take much to be able to smell it. The question I have is if it was releasing a lot more when it wasn't adjusted properly and likely took a lot longer to light, if that made you more aware of it and now you are overreacting to a normal amount or if it is still taking a long time to light. You could look in the combustion chamber through the site glass as it is lighting and see how long it is between when you hear the valve open and when you see a flame. Since i think the burner in there is sort of a grid it probably takes a few seconds for the flame to spread across that grid and it may release some unburnt gas while that is happening.

EBEBRATT-Ed

@svuk15

PVC pipe and fittings are pretty cheap. Why not raise it and see what happens?

It could be due to being inside the fenced in area.......maybe your getting a weird down draft or something.

Many times a chimney problem show up when they previously had no issues. But trees grow over chimneys and cause problems.

Part of troubleshooting is to find the problem you have to rule out other issues

Or live with it, there is most likely no majic fix

Driven11

mattmia2 said:

I don't think it would be unusual to release a small amount of unburnt gas when it first fires as it is lighting. It doesn't take much to be able to smell it. The question I have is if it was releasing a lot more when it wasn't adjusted properly and likely took a lot longer to light, if that made you more aware of it and now you are overreacting to a normal amount or if it is still taking a long time to light. You could look in the combustion chamber through the site glass as it is lighting and see how long it is between when you hear the valve open and when you see a flame. Since i think the burner in there is sort of a grid it probably takes a few seconds for the flame to spread across that grid and it may release some unburnt gas while that is happening.

It definitely doesn't take much to smell it. I read something ages ago about the chemical they add to the gas being chemically related to the smell of rotting meat/death. Something we are extremely sensitive to and equate with bad things. Gets your attention in a hurry.

dmd518

Thank you so much for posting this. I am actually dealing with this now (240A) and experienced similar feedback from my contractor. I am curious what DIP settings were changed that resulted in the error being correct, can you please share? Thank you!

JohnNY

This past week I was called to work on a Navien Combi that was poorly installed. It smelled of gas when I finally got it to run, but it would dissipate shortly after, but again, nearly every time. I called Navien and told them what it was doing and they assured me that was normal operation for Navien.

Solid_Fuel_Man

I would do a leak check of the gas valve for longer than 10 min. If a small amount of gas is leaking by into the combustion chamber, then during pre purge it would be blown out the exhaust and smell. 

Agrimm

I'm aware this is an old post but found this forum as a result of searching online for this exact issue. I've recently had a Navien tankless installed (replaced my Rinnai).

I live south in a temperate climate - so mine is exterior mounted & vented through face of unit. Installed same location as previous - but never had any unburned gas smell. I am getting that during start up of this unit frequently.

OP - was there any further help from Navien? Any others with this issue know if I should be concerned or if this seems to be typical of these Navien units?