Navien NPE-240a shuddering/vibrating from intake

[J12345]

Hi,
I have a Navien 240a that has started shuddering and shaking when under full load running the bathtub. No error codes. In taking the cover off, it’s clearly an issue related to the intake air, almost as if it’s gulping for air and quickly starving and recovering several times a second. Cover on or off makes no difference. You can see this when looking through the viewer at the burner as well. Oddly, if you just place a finger or other slender object above the intake and disrupt the air flow, the shuddering and shaking and noise all stop and it sounds normal. This is right above the actual intake with the cover off. What I don’t know is if by placing something in the air flow path it is disrupting the flow (ie laminar vs turbulent) or if when you do that, the controls are somehow compensating something else that causes it to smooth out. I can certainly call a plumber, but I’ve had mixed luck in the past with their experience on this unit. I’m a mechanical engineer so technical troubleshooting isn’t an issue if the experienced folks on here have any ideas.
Thanks!

 

[FDNY/RETIRED]

I am not a Navien expert or a plumber. I have a NCB-240e and have been coming here trying to figure my own problems out. So with that let me ask a couple of questions. But let me say right off. I really do not understand why it smooths out when you disrupt the air flow.
1.How old is the unit?
2. You say only on the bathtub under a full load. I am sure it also controls other faucets and appliances. Does it do it on any other faucets or appliances under a full load?
3. It's only under a full load?
4. NG or LP gas?

Now the first things I would check is air filter. Is it clean and there are no obstructions in the intake line. Or any debris on the fan or broken blades? Causing a imbalance only under a full load. I am not sure what the fan unit looks like, so I am taking a wild guess. Is this what your unit looks like?


You say you can see the flame increase and decrease. So again not knowing how long you have had the unit maintained. A wild guess would be something happened to the gas flow input. I would check the WC measurements. My thinking is a low gas supply might make it seem that it is a intake problem. But it could be a gas problem or if you look at the exploded view. Part #23. Air Pressure sensor might have a problem. Or can there be a air leak someplace and like with a carburetor by decreasing the air flow. By placing your hand over it. You can make it idle smooth?

Maybe this will help give you a couple of ideas what to check, if you have the equipment. Again I am only a homeowner no expert.

 

[Sponsor]

 

[J12345]

I am not a Navien expert or a plumber. I have a NCB-240e and have been coming here trying to figure my own problems out. So with that let me ask a couple of questions. But let me say right off. I really do not understand why it smooths out when you disrupt the air flow.
1.How old is the unit?
2. You say only on the bathtub under a full load. I am sure it also controls other faucets and appliances. Does it do it on any other faucets or appliances under a full load?
3. It's only under a full load?
4. NG or LP gas?

Now the first things I would check is air filter. Is it clean and there are no obstructions in the intake line. Or any debris on the fan or broken blades? Causing a imbalance only under a full load. I am not sure what the fan unit looks like, so I am taking a wild guess. Is this what your unit looks like?
http://www.navienparts.com/media/7. NR_NP Components Diagram and Parts List (1).pdf

You say you can see the flame increase and decrease. So again not knowing how long you have had the unit maintained. A wild guess would be something happened to the gas flow input. I would check the WC measurements. My thinking is a low gas supply might make it seem that it is a intake problem. But it could be a gas problem or if you look at the exploded view. Part #23. Air Pressure sensor might have a problem. Or can there be a air leak someplace and like with a carburetor by decreasing the air flow. By placing your hand over it. You can make it idle smooth?

Maybe this will help give you a couple of ideas what to check, if you have the equipment. Again I am only a homeowner no expert.

good suggestions. To answer a few and provide some more details. Perhaps “full load” isn’t accurate, but high load would be a better description. Yes, other fixture usage if combined for high demand produces the same effect. The unit is about 3 years old. After observing it some more, I think blocking or obstructing the airflow is causing it to have restricted flow and it adjusts gas accordingly to keep the mixture correct. I suspect your thought of the gas input being the issue is correct. About 8 months ago The unit was experiencing combustion in the exhaust a couple of times a week. The techs that came out couldn’t find anything wrong with it, but in a forum online someone suggested that they had this problem and that putting a gas pressure regulator in line is what navien recommended. We tried this and it has worked fine with no exhaust combustion (think potato gun) and this shuttering did not exist until now. What is interesting is that when they did this, they initially put a regulator on that did not support the needed flow and the unit had similar issues. They replaced it with an upsized regulator and all has been fine for months. Long story short, I need to call them back and have them check incoming pressure and supply. I’m a bit confused to why it wouldn’t throw an error code in this scenario though or what may have changed in the past 8 months.

 

[FDNY/RETIRED]

For some reason I didn't get an update to your thread. I have to look to see if I didn't set it up right for updates. I watched a friend with a NPE 240 a less then 9 months old. Actually 2 of them and one was doing what yours did. I was impressed with the setup. Like I said the same problem you are having started a month before Christmas. Got real bad about a week before Christmas. Hold nothing but a piece of coat hanger wire over it and it smoothed out. He had a tech come over and the guy replaced the Air Pressure Sensor all was fixed.


Yep I didn't have it set to receive email notifications.

 

[J12345]

For some reason I didn't get an update to your thread. I have to look to see if I didn't set it up right for updates. I watched a friend with a NPE 240 a less then 9 months old. Actually 2 of them and one was doing what yours did. I was impressed with the setup. Like I said the same problem you are having started a month before Christmas. Got real bad about a week before Christmas. Hold nothing but a piece of coat hanger wire over it and it smoothed out. He had a tech come over and the guy replaced the Air Pressure Sensor all was fixed.


Yep I didn't have it set to receive email notifications.

Thanks for checking in!
I ended up having the plumbing company who installed the unit come out. They worked over the phone with Navien to troubleshoot and arrived at the conclusion that the unit couldn’t handle the incoming temperature delta with the cold water coming in and high demand. They ended up restricting the cold water inlet by partially closing the valve. It has worked, however, it’s clear that the flow has been reduced when you run the tub on max. This doesn’t really make sense to me since you would think it should still be able to run at its max and the only negative of not being able to handle the temperature delta would be cooler output water. Additionally, this is year 3 and we never had this problem previously. With what you stated, I may try replacing the pressure sensor since it’s quite simple and see if that resolves.

 

[FDNY/RETIRED]

Like I said I am no plumber or expert by any means. But that is the weirdest thing I ever heard of. An external water supply regulator is one thing. I know on my Travel Trailer that I lived in while they elevated my house. I had to use an in-line water regulator to decrease water pressure. I did change it to an adjustable one later. I have no idea how your water is supplied by well or municipal. You’re like only 600 to 1200ft above sea level. Unless you live on top of Eagle Mountain. But if you never had problems it sounds like a band aid fix. Which down the road might be a bigger problem.

Aren't there water flow restrictors that you can screw into the unit? Mine came with 4 different ones. The orange one in my unit gives my 5.6 GPM to my faucets. Even though I have a Mod/Con the restrictor is still on the Cold-water supply inlet. They also said I didn't need a external regulator because I have the restrictor and a internal regulator with a makeup water feed system. I would think incoming water pressure even on your unit is regulated. That it would regulate cold water coming in. To allow the cold-water heat to hot water temp in your unit to 120-130F. Regulate max demand from your faucets at least 5.6 GPM. Again, I do not want to give the wrong info to you. Usually, it is a starvation for water that I see throw the codes, or cause over boil in any type of unit. Or a temp sensor not working that causes over boil problems. There might be something I am not figuring into the equation. But to me restricting incoming water the way they said doesn't seem to be the way to go.