Lochinvar boiler howling after DHW call

ajustin

I recently built a house and installed a radiant floor heating system with an indirect DHW tank. I am a commercial plumber by trade, so my knowledge of heating systems isn't the greatest so I will do my best to explain the setup and issue.
I have a Lochinvar Noble 80K boiler with the 40 Gallon Squire indirect tank with wired tank sensor. The system is piped with zone circulators controlled with a Taco SR504 board setup for DHW priority. Everything with the system is working great except for an annoying howl coming from the boiler from a low flame after a satisfied call for DHW switching to a space heat call. So here's what happens...

While the boiler is heating for a space heat call the DHW calls, the Boiler increases the setpoint to 160* and the Taco board kills power to the space heat circulators and powers the DHW circulator. The boiler heats the DWH to the 120* setpoint and ends the call for heat. The Taco board then kills power to the DHW circulator and powers back up the space heat circulators. Meanwhile the boiler reduces the heating setpoint to 110* or whatever it has adjusted to based on the outdoor temp. This is when I get the howl, the boiler is modulated to 10% while the input temp drops to where it needs to start heating again. The display will show low flame current on and off during this time and it makes a howling sound that fades in and out.

There seems to be no way to adjust the minimum modulation settings on this boiler. It seems like the boiler should shut down and lockout until the input temp lowers before resuming the space heating call but I can't find any way to do that.

Hopefully this makes sense and I can get some input because I'm sure the neighbors don't appreciate the noise. Thanks for the help.

ch4man

your burner set up needs to be tuned with a manometer and combustion analyzer. the boiler must burner clean (no/low CO) on high fire, low fire and all inputs in between.
yours doesnt sound like thats happening.
find someone who not only has a combustion analyzer but also knows how to use it properly.

you very well may be making God awful amounts of carbon monoxide. bad, real bad

hot_rod

Here is the setup procedure for the burner. I'll bet there are some YouTube videos or a trainer at the Lochinvar site to guide you through. You need an analyzer that has been accurately calibrated to dial it in.

psb75

I am having exactly this same problem with new Lochinvar Noble 80. There is same "howling" going on as it ramps down to low modulation. Some kind of exhaust resonance. I don't even have the DHW indirect tank and circuit hooked up yet. It is only doing heating on radiant panel circuit. This has been going on since I commissioned the boiler several months ago.
I have spoken to Lochinvar tech 3 times already. I set the boiler up originally with combustion analyzer and got it right within target ranges for low and high fire. I have adjusted it again, even closer to the specified target ranges. The howling continues.
The latest talk with the Loch. tech said that getting the boiler set at the specified ranges "wasn't good enough" if the boiler was still howling. He said to "adjust the boiler when it was howling" .
The homeowner and I are getting quite annoyed with the sound of the boiler.
I also have been instructed to change out the small circuit board that the outdoor sensor is connected to, because I have never been able to get the boiler to recognize the sensor.
This is my first time installing a Lochinvar boiler. NOT my first time installing mod cons though. I have done TT, Viessmann, NTI, Laars, Rinnai, Buderus. I judge a company on its tech support. As well as its equipment.

Jamie Hall

The howling may be a combustion problem, and there's no point in playing with anything until that is right. But... it may also be a resonance in either the intake or exhaust piping as well (which isn't going to help the combustion numbers either, by the way). To get a little more insight into that, try dialing the combustion rate up and down slowly, and see if there is a rate -- or a narrow range of rates -- at which the problem is worst. That will point you to a resonance in the piping (think poorly setup organ pipe). If the howl has a more or less defined pitch, that may help locate the offending pipe.

psb75

I've tried putting restriction on first, the intake and then the exhaust (3"-2" reducer)--to no discernible effect. I was thinking that would maybe upset or muffle any resonance. No luck.
The resonance seems to happen only when the boiler is modulating in its normal heating modes. It doesn't make the sound when the boiler is manually run with me standing in front of it with my combustion analyzer and controlling the fan speed.
I do know that it happens when the fan speed is slowing down from a higher fire rate. It is a strange intermittent howl that I have never heard before from a mod con boiler.
It is definitely some kind of combustion noise and I'm unable to pin-point the offending source.
It howls loud enough to wake up the occupants of the house next door at night.
The only encouragement that I'm not incompetent at solving this, is that there is ANOTHER person experiencing the same syndrome...on this forum.
I have spent enough time at trying to solve this with an analyzer and ph. calls to Lochinvar...that I prob. won't install another one of these.

Jamie Hall

A restriction won't affect the resonance. Changing the length of a pipe will.

Leon82

They have a minimum vent length for some of their boilers in the manual. The wh series was 12 feet

hot_rod

The latest talk with the Loch. tech said that getting the boiler set at the specified ranges "wasn't good enough" if the boiler was still howling. He said to "adjust the boiler when it was howling" .
The homeowner and I are getting quite annoyed with the sound of the boiler.

I sat in on an NTI training recently, they mentioned this procedure also when trying to tune out a stubborn noise.

Did you try this? I'd imagine every mod coin boiler brand would give you the same response for this problem?

Trust me it is not a brand specific problem as dozens of brands use this some combustion method.

ajustin

> @Leon82 said:
> They have a minimum vent length for some of their boilers in the manual. The wh series was 12 feet

In my case that shouldn't be an issue. Manual specs 7' as the minimum and I have about that in straight pipe plus multiple 90's.
Thanks for the input. I will look into the combustion possibly being the issue.
Does anyone know if these boiler's software can be updated with additional parameters that would allow a little more control? This Noble seems to be a little lacking on that compared to the Knight series.

ch4man

ive had the same howling on a 50's vintage natural draft furnace with slotted cast iron burners before. adjusting the primary air shutters cured that.
most all of the manufactures instructions on setting up mod/cons involve the throttle screw.
fuel air ratio
but sometimes you need to get into the super secret screw and get into the manifold gas pressure that is not really measured as these style boiler use a negative pressure regulator in the gas valve. most mfgs dont want you going there. i call it the super secret screw as done wrong you can really mess it up

Zman

I would try adjusting it to the rich end of the range. Go for the lowest O2 number in spec without sending the CO though the roof. A similar noise will sometime occur caused by harmonics though the gas pipe, especially when the house regulator is very close to the boiler.

psb75

Thanks Zman. I will try this suggested, further adjustment (see paragraph below). Interesting point about gas pipe harmonics. The house regulator is more than 10' from the boiler --which the manual specifies--but not by much. It is probably 12'.
Also interesting ch4man, about "the secret screw." Lochinvar has TWO adjustment options on the gas valve. 1.) the easily accessible, larger 4 mm hex, "bias/offset adjustment screw" (top center of gas valve) for "low fire" adjustment, and 2.) the more "secretive" and harder-to-access, smaller 2.5mm hex, "throttle adjustment screw for "high fire" adjustment. This one is not so easy to adjust with my Allen key set. I would definitely call it "secret." :-(

rick in Alaska

I also have one of those noisy Lochinvar KHN's. Been trying to figure it out for quite a while now, and still haven't figured it out. Apparently, it is one of the original ones, and might require a newer control board. I do know they like to see the co2 at around 9.15, as a genera rule. Also, there is a flapper in the intake that you want to make sure is clean, and moves easy.
I wonder about a flex gas line connector. I have heard that other than hard piping the line, that some times you can stop the noise by just moving the flex line around.
Other than this one unit, I love the Lochinvars and will keep on installing them.
Rick

andymercury

Don't mean to rehash an old thread, but I am also having this same issue with a KHN110. Runs perfectly until it modulates down to 10% after a call for DHW has been satisfied. It starts howling and vibrating. Sounds like the flame is flickering (best way I can describe it?) but it is a very loud rubling/howling noise. It has been doing this since I installed it a couple years ago. I have tried all of the above, and double checked the installation 10 times. I do not have a combustion analyzer and would appreciate a recommendation for a competent tech in the RI area (I am a marine tech and know how few and far between good techs are). I do not have a lot of faith in the combustion adjustment fixing this issue though, as it seems this has been tried by others many times with no success (both on this thread and others I have seen here). Has anyone ever solved this issue? Sounds like a common one with this model. I am debating trying a gas valve, but would rather not take a $500 shot in the dark without some opinions first. Wish I could limit the minimum firing rate to 12% or so, as this only seems to happen at the lowest rate of 10%. Thank you for any input!

rick in Alaska

You absolutely have to adjust the gas valve at high and low fire or it will do what you describe. You might also check the air intake for blockages, although I am pretty sure you have looked at that.
One other thing to look at is the little barbed fitting in the air intake that the little hose attaches to. Take the fitting out and make sure it is the one with a hole in it that is almost full size. The earlier ones had a really small hole that caused some issues.
Did I mention having the gas valve adjusted? Yep, I did. it is a must.
Rick

psb75

I had this problem with a newly installed Lochinvar Noble 80 (not the combi). This was two years ago. The problem was persistent. Myself and local regional rep could not solve. Had one come up from MA headquarters in the official Loch. truck. I ended up replacing two motherboards that this tech had "tweaked" at the home office and sent to me (this was because of Covid, to minimize trips to site). He made the boiler "skip over" a certain troubling fan-speed as it was ramping up and down. There was a very loud and disturbing "howling/fog-horning" that was happening at lower fire. That solved the problem and the client's were no longer woken up at night by the "howling" boiler.

Ironman

I have well over a hundred hours dealing with “fog horning” on different brands.

The problem is caused by the use of CSST in the gas line. Remove or increase the size of the CSST and the problem should go away.

Adjust the fuel to air ratio to the richest value that the manufacturer allows.

psb75

I have never (and never will) use CSST for boilers. 'Near appliance' hook-ups, yes. Just the short connectors.

HomerJSmith

Get a mechanic's stethoscope from an auto parts house and use it to pin point the source of the noise. Might help your diagnostics.

mattmia2

Maybe several feet of very large, maybe 1.5" or so black iron at the inlet to let the gas slow down and settle down before it gets to the boiler?

andymercury

Thanks for the suggestions guys!

@Rick in Alaska

I just checked the fitting and it is a full size opening in the brass fitting. I will certainly have a tech come out and make the combustion adjustments.

@psb75
It would be awesome if I could change the minimum fire rate to like 12%.  A couple percent is all I would need.  If it were only that easy!  Sounds like what you were experiencing is exactly what I am seeing.  Howling/fog horning. 

Ironman said:

I have well over a hundred hours dealing with “fog horning” on different brands.

The problem is caused by the use of CSST in the gas line. Remove or increase the size of the CSST and the problem should go away.

Adjust the fuel to air ratio to the richest value that the manufacturer allows.

 @ironman
I do not have any csst in the system.  All black iron; 1" feed reduced to 3/4" 3' from the boiler, and reduced again to 1/2 at the gas valve inlet
 

andymercury

HomerJSmith said:

Get a mechanic's stethoscope from an auto parts house and use it to pin point the source of the noise. Might help your diagnostics.

The source of the noise is the flame "flickering" for a lack of better term. 

andymercury

@ajaustin
Did you ever resolve this issue?  You are describing literally the exact same issue I have

Zman

@andymercury
Have you had a combustion analysis done? Did they adjust it to the rich side of the spec?
What size and type gas line do you have? How far is it from the boiler to the house regulator?

HomerJSmith

I'm thinking there is a rubber coupling between the air intake and the blower motor.

Disconnect the rubber coupling and let the boiler draw combustion air from the room and see what happens at very low fire.

andymercury

Zman said:

@andymercury Have you had a combustion analysis done? Did they adjust it to the rich side of the spec? What size and type gas line do you have? How far is it from the boiler to the house regulator?

I am working on getting a tech here for a combustion analysis.  All black iron; 1" feed reduced to 3/4" 3' from the boiler, and reduced again to 1/2 at the gas valve inlet.  Approx 30' from the main regulator.

HomerJSmith said:

I'm thinking there is a rubber coupling between the air intake and the blower motor. Disconnect the rubber coupling and let the boiler draw combustion air from the room and see what happens at very low fire.

I will give that a shot tomorrow and report back.  I have also double checked for intake and exhaust restrictions.  I have tried a 3" to 2" reducer first on the intake and then the exhaust pipes as suggested on another thread also.

psb75

I did combustion analysis, two different Loch. (local and regional) techs did combustion analysis. I put on and took off various vent and intake restrictions--all to no effect. Problem was corrected on the motherboard by the main tech in the main office. No more howling/foghorning.