My Utica MAC 205 Boiler Sounds like the Horn of Gondor

Prevch

I had a new boiler installed in 2018. Basically nothing but problems since it was installed. It kept kicking off and erroring out. We eventually found out that the installer undersized the gas line, but we found that out after working with multiple heating contractors who had taken apart the unit several times, which led to the unit leaking. We ordered a new gasket for it and used a gas sniffer tool to ensure we had no propane leaking out, everything checked out fine once the new gasket was installed.

That being said, ever since (or at least fairly close to that time) the boiler had been taken apart and put back together several times, it periodically sounds like the Horn of Gundor when the flame kicks on. Now, when I hear the word horn, I think air, but again, we cannot find any leaks. Also, it does not happen every time the boiler kicks on. It is bizarre. It does seem to happen frequently when the unit switches between heating domestic water and radiant floor water, but not every time and that is not the only time it happens. It also often happen when a new zone kicks on, but again, not every time. My best guess scenario at this point is that when cool water hits the hot resevoir, it is causing the unit to resonate, and it does also kind of sound like that as well, but that is only a guess.

No one seems to be able to give me a definitive answer on this and Utica won't talk to me because I am not an HVAC person. And, where I live, getting an HVAC person, or any other professional to show up at your house, is literally almost impossible.

So, I am at a loss. Do you think there is any relation between the disassembly and reassembly of the unit with the sound, or is that just a coincidence? Do you guys have any ideas or troubleshooting steps you think I should try? The manual does not say anything about this issue in the troubleshooting section. Any help you could provide would be awesome!

Jamie Hall

Since the undersized gas line was the first thing that should have been checked, not the last (gas pressure when firing), I don't have much confidence in the folks you are working with.

That said, how is the gas connected to the boiler? There have been a number of problems with boilers connected with flexible (CSST) gas lines which are similar to yours. I've not personally investigated them, but some kind of resonance between the change in gas flow and the line losses seems to cause a flame instability which sounds like a horn.

So -- how is yours connected?

Prevch

Jamie Hall said:

Since the undersized gas line was the first thing that should have been checked, not the last (gas pressure when firing), I don't have much confidence in the folks you are working with.

That said, how is the gas connected to the boiler? There have been a number of problems with boilers connected with flexible (CSST) gas lines which are similar to yours. I've not personally investigated them, but some kind of resonance between the change in gas flow and the line losses seems to cause a flame instability which sounds like a horn.

So -- how is yours connected?

Interesting. Mine is indeed hooked up with flexible line. I will provide pics when I get home. I also should add that, rather than running a new, larger line, to fix the undersized line issue, a 2lb regulator was put on the house. Then, right before the boiler, there is another regulator to kick the pressure down to where it should be per boiler spec. Again, I will provide pics when I get home.

Kickstand55

I had a situation years ago where a Utica LP Gas boiler was in service for many years and this occurred. Not sure if it is the same model as yours. Nothing had changed about the home.
Checked the chimney, draft, room air supply, all good. The flame was burning within the tubes causing resonation.
After checking, the inlet pressure was too high, the Gas Provider replaced the regulator. Then set manifold pressure to spec., nothing changed.
Called Utica Tech support. Their answer was a superseded burner tube(s) for that boiler, which they sent. Replaced, set parameters to spec., still to no avail.
I left the company and did not find the answer.
Best to call Utica Tech support for help.

Ironman

The CSST is your issue.

https://forum.heatinghelp.com/discussion/164856/csst-the-cause-of-harmonic-fog-horn-noise#latest

Prevch

Ironman said:

The CSST is your issue.

https://forum.heatinghelp.com/discussion/164856/csst-the-cause-of-harmonic-fog-horn-noise#latest

So if I go with 1" CSST that would fix it? Otherwise, I would need to just go with black rigid pipe and that shoudl fix it?

Prevch

Kickstand55 said:

I had a situation years ago where a Utica LP Gas boiler was in service for many years and this occurred. Not sure if it is the same model as yours. Nothing had changed about the home.
Checked the chimney, draft, room air supply, all good. The flame was burning within the tubes causing resonation.
After checking, the inlet pressure was too high, the Gas Provider replaced the regulator. Then set manifold pressure to spec., nothing changed.
Called Utica Tech support. Their answer was a superseded burner tube(s) for that boiler, which they sent. Replaced, set parameters to spec., still to no avail.
I left the company and did not find the answer.
Best to call Utica Tech support for help.

That is not encouraging lol

Ironman

Prevch said:

The CSST is your issue.

https://forum.heatinghelp.com/discussion/164856/csst-the-cause-of-harmonic-fog-horn-noise#latest

So if I go with 1" CSST that would fix it? Otherwise, I would need to just go with black rigid pipe and that shoudl fix it?

I can’t guarantee that because I don’t know the particulars of you house.

Gas line sizing must be done according to code using approved charts and calculations for the specific application.

There’s no “one size fits all” method.

What I am trying to point out is that the CSST is the cause of the fog-horning.

Prevch

Kickstand55 said:

I had a situation years ago where a Utica LP Gas boiler was in service for many years and this occurred. Not sure if it is the same model as yours. Nothing had changed about the home.
Checked the chimney, draft, room air supply, all good. The flame was burning within the tubes causing resonation.
After checking, the inlet pressure was too high, the Gas Provider replaced the regulator. Then set manifold pressure to spec., nothing changed.
Called Utica Tech support. Their answer was a superseded burner tube(s) for that boiler, which they sent. Replaced, set parameters to spec., still to no avail.
I left the company and did not find the answer.
Best to call Utica Tech support for help.

That is not encouraging lol

Ironman said:

Prevch said:

Ironman said:

The CSST is your issue.

https://forum.heatinghelp.com/discussion/164856/csst-the-cause-of-harmonic-fog-horn-noise#latest

So if I go with 1" CSST that would fix it? Otherwise, I would need to just go with black rigid pipe and that shoudl fix it?

I can’t guarantee that because I don’t know the particulars of you house.

Gas line sizing must be done according to code using approved charts and calculations for the specific application.

There’s no “one size fits all” method.

What I am trying to point out is that the CSST is the cause of the fog-horning.

Got it. Thanks

Prevch

Here are some pictures. I would say that there is about 50ft or so of 3/4" flex pipe that runs from the 2lb regulator outside to the regulator you see in the pictures. From the regulator in the pictures, there is solid 3/4" pipe which runs into the boiler @Ironman

Ironman

I’ve never dealt with a fog-horning situation where the CSST was on the supply side of the regulator, so I’m not sure if the harmonics will transfer through the regulator.

I have seen where it can happen when the regulator is too close to the appliance, like you have it.

It’s recommended to have at least 10’ of hard pipe between the regulator and the boiler or fog-horning can occur.

P.S.
I do remember a situation like yours from about 15 years ago where the gas contractor did the same thing and it fog-horned. I don’t think the owner ever made him correct it.

GGross

@Prevch
This might not have anything to do with the horn of gondor (lmao) but the length of pipe from that second stage regulator to the boiler is most likely going to cause you issues in the future. I had 1 manufacturer tell me no less than 6 feet of 3/4" pipe (we were locking out on failed ignition) but In my experience we needed more, that was for a 155,000 BTU boiler. In addition to being able to deliver the proper amount of fuel, you also need to guarantee the initial volume of fuel at ignition to prove flame. It won't always be an issue, but if you start locking out on failed ignition, that would be the most likely reason in my opinion.

edit: I see @ironman already suggested this, pretty smart guy!

Prevch

@GGross @Ironman Interestingly, the Horn of Gondor started sounding long before that second regulator was put in. It started happening after we found the propane leak from the boiler being taken apart. The 2lb regular outside and regular you see in the pics above weren't installed until probably a year after that.

So, if it was you, what would you do? Bear in mind that calling a professional is pretty much not an option. Maybe I just run 1" black pipe from the 2lb regulator to the regulator inside and create some extra space between the inside regulator and the boiler?

Or perhaps I should try knocking the pressure down a 1 or 2? I can't remember off the top of my head, but I think my boiler is rated for 8-12, and it is currently at 12, so perhaps ease off to say 10?

Any other ideas?

ch4man

if, as you say calling a professional not an option then you'd best purchase a $1000 combustion analyzer and spend another grand on training, take a minimum of two years HVAC training so you can dial in the fuel/air mixture to stop this. CSST is not the only cause. sorry

Prevch

ch4man said:

if, as you say calling a professional not an option then you'd best purchase a $1000 combustion analyzer and spend another grand on training, take a minimum of two years HVAC training so you can dial in the fuel/air mixture to stop this. CSST is not the only cause. sorry

Don't get me wrong, I would love for a professional to handle it, we literally can't get one to show up and in the off chance we do get one to show up, they have no clue.

pedmec

I would have someone come out and do a combustion test. Improper combustion will cause the foghorn noise your talking about. Happens when the gas pressure is to low in low fire after modulating down. Should always do a combustion test when adjusting gas pressures.

GGross

@Prevch

I would schedule a service call, tell them you need to have about 10' of solid pipe between reg2 and the boiler, and have them properly tune combustion after changing the gas piping

Prevch

GGross said:

@Prevch I would schedule a service call, tell them you need to have about 10' of solid pipe between reg2 and the boiler, and have them properly tune combustion after changing the gas piping

I will give it a shot and let you know. We will se if I can get someone to show up!