oil boiler loud drone when firing

epmiller · February 21

I am not an oil tech so I don't know if this is a problem or not. I went to take care of my neighbor's dog and when I left myself in the house there was a loud droning sound, so loud I immediately went to the basement to see what was going on. The boiler is a really old unit, it looks like the gun is not removable, welded to the combustion chamber door. The hum is around 69 hz and between 75 and 80 db. Is this something that is immediately dangerous or can it wait 10 days or so until he comes home? Knowing how little he is home, this likely has been going on before I showed up. I just don't want to ignore it if it is immediately dangerous.

EdTheHeaterMan · February 21

Insufficient evidence to make a determination. Droning noise? I can only think of the noise a Drone might make when it is flying too close to you. That is not an oil burner noise that I am familiar with. Now if you shut off the switch that powers the burner and the noise stops. then you know for sure that the noise is from the heater and not something else like a sump pump or exhaust fan that is stuck on. is this the noise?

https://www.youtube.com/shorts/FGnRJlfecC4

HVACNUT · February 21

Can you contact him? Tell him about the hertz part. That might get him to get it checked out, pronto. I feel bad for the dog.

Jamie Hall · February 21

Is this hot air or hot water or steam? If it's a steady hum or drone, my bet is going to be on a fan — but which fan, and how much of a problem it is, depends on what kind of unit it is.

Big Ed_4 · February 21

One thing to check is back pressure…. Lack of draft ?

HVACNUT · February 21

Bad bearing assembly on a 3 piece resonating through the pipes.

epmiller · February 21

@EdTheHeaterMan @Jamie Hall Sorry I wasn't clear enough, it's an oil burner, 3 circulators on a hot water system. I don't service oil burners I only have installed gas mod-cons so I understand the hydronics part and yes, it sounds like a loud toy drone aircraft, although to be this loud it must be 150lbs with 3ft rotors right beside you.

@Big Ed_4 I don't have tools for oil burner work. This is a really old 150-170kBTU input boiler, looks like 10' or so of 6" galv smoke pipe going into a probably 12" glazed thimble (which has a hairline crack per my check last night). I'll have to go back and look, I can't recall seeing an atmospheric damper on that pipe either. It wouldn't surprise me on lack of draft, but this thing is serviced by a very large oil dealer and seeing some of the workmanship I don't trust that last service. Nothing noted except a valve was replaced. The tech LOVES his ProPress, ten fittings where three would have done. I have not noticed this drone any time last heating season when I was taking care of his dog.

@HVACNUT the dog is old and deaf. She can't hear me clap my hands 3 feet away. 😕

So I'm taking it that it isn't dangerous. I won't interrupt his vacation. If the boiler goes down I'll know it before anything freezes.

EdTheHeaterMan · February 21

To the technical folks @epmiller — your noise description was very specific. I even went online to find a comparison tone. The frequency wasn’t an exact match, but the volume level was close to what I’m hearing.

Regarding oil burners, that is not a normal operating sound. It’s possible the noise is combustion-related. I’ve heard this before when servicing a burner that is not adjusted properly — we call it pulsation.

Pulsation occurs when the rapid expansion of combustion gases creates back pressure against the combustion air fan. That back pressure can cause incomplete combustion, which then reduces chamber pressure and allows more combustion air in. The mixture improves, combustion becomes more complete, pressure builds again — and the cycle repeats.

This expansion and contraction can occur anywhere from about 10 cycles per second to over 30 cycles per second, producing a very distinct and sometimes loud noise.

If the burner is pulsating, that is not normal and should be addressed. A qualified service technician should inspect and correct the issue.

mattmia2 · February 21

what type of burner is it, is it a modern power burner type oil burner or is ot some very old design that became obsolete around the 60's?

MaxMercy · February 21

You can shut the oil off while the burner is running and see if it's combustion related (you may have to bleed it after that test). If it still drones after the flame stops and before it locks out, it could be the burner motor getting loud.

Circulators also make loud whining/shrieking sounds when they are close to EOL. You could try shutting down each zone by the thermostat and see if one of the circs is creating that noise. The noise circs make often gets telegraphed through the whole piping system and can throw the source of the noise off.

Jamie Hall · February 21

@EdTheHeaterMan has an interesting point — and if the tone is quite steady at the specific pitch it could well be pulsation from combustion.

Big Ed_4 · February 21

If you open the fire inspection door and the noise stops then its combustion and draft. …

epmiller · February 22

@mattmia2 this is a very old burner, probably the original boiler with the house and that is a good bit older than I am. The way it is mounted you couldn't replace it with a modern gun, there is a tube welded to the fire door and the gun is mounted out at the end with a grub screw thru a short collar on the gun.

@MaxMercy the sound goes away the instant it stops firing. The one circulator is a bit noisy but this noise isn't that. There's no way in my experience that a circulator can be that loud at that low frequency.

@Jamie Hall @EdTheHeaterMan's explanation makes a lot of sense, I'm going with that. I will stick to my 68-70hz frequency, I have done audio work for more than 50 years and I have tools on my phone to do the analysis. I went down this morning and the burner happened to fire while I was looking at the system. The noise wasn't bad when it started firing but got loud after about a minute. I isolated the area of the audio spectrum where the drone occurs and it is right at 100db, the complete spectrum (20-20kHz) it is only in the mid 70db range near the boiler and I'm getting no other peaks in the spectrum like a whining circulator or bearing would show.

@Big Ed_4 I will try that tonite when I go to take care of the dog. Thanks all, I've learned something. I'm going to keep tabs on it and recommend he get service when he gets home unless someone here tells me that it is immediately dangerous or catastrophic.

EdTheHeaterMan · February 22

I'm going to keep tabs on it and recommend he get service when he gets home unless someone here tells me that it is immediately dangerous or catastrophic.

without looking at it personally or hearing it on a video, I can't tell you for sure that it is immediately dangerous or catastrophic. But on the same note if it is the pulsation I described is what is happening, then I would look into this problem tomorrow, not in a week or so.

If the noise is not pulsation, then you can wait longer. If you feel daring, and you can locate the flame inspection door, and you can open it, and the pulsation stops, then you can decide from there.

This site does not support video upload, but if you can shoot a video and post it on youtube or facebook or some other platform. post the link to the video and I can listen to the noise and give you a better answer.

Pulsation can end up with a sooty mess inside the boiler and eventually end up with a lot of soot damage thru the entire home if you let the problem go too long.

Big Ed_4 · February 22

No good deed goes unpunished … :)

EdTheHeaterMan · February 24

Is this your video if the droning noise? If yes, that noise is not a combustion noise.

https://www.youtube.com/shorts/iBMdga_hM2A

If NO then the link you send is not a good link

Jamie Hall · February 24

Nor is it a flue resonance…

epmiller · February 25

I'm not certain what happened to the post of my link. Here it is again. My phone evidently didn't like it. The noise is more pronounced about 2/3 of the way thru the video. It wasn't nearly as loud when I took this as the first night I was taking care of the dog. I could hear it on the second floor then, now only on the first floor.

https://www.youtube.com/shorts/bs5Jjs_4aeg

Sorry all, I have been too busy to get back before this.

Jamie Hall · February 25

Almost sounds like a wonky bearing driving something to vibrate. Maybe some sheet metal or light metal object slightly loose.

epmiller · February 25

@Jamie Hall the main reason I don't think it's a bearing is that the sound goes away the instant the flame stops. I've stuck my head down closer to the gun and I can't hear anything that makes me think bearing. The "smoke pipe" is vibrating but it's screwed together and not rattling. It's going to wait until the owner gets home.

@Big Ed_4 as you can see in the video the flame inspection door is cemented shut. I wish I could try opening that, it makes sense that a change in the combustion chamber air could change the burn. This thing also doesn't have an atmospheric damper, curious why not.

Big Ed_4 · February 25

Combustion and draft .. It could be the lack of a draft regulator , Looks like the guy that installed the chimney liner left it off … I believe the boiler might be a three pass boiler . I hear the venting pulsating .. The Carlin burner 40+ years old ..

HVACNUT · February 26

Sounds like a Didgeridoo. Definitely combustion and/or draft related. Looks like a positive pressure boiler.

EdTheHeaterMan · February 26

Dynatherm Boiler is a positive pressure boiler that has fire tubes from the back of the boiler that run back to the front pan shape cover that the burner is welded on, the the flue gasses are directed under the boiler to the flue outlet near the opposite end of the boiler from the burner.

That particular vibration is a combustion noise and is resonating that vibration thru the vent connector pipe. A minor air adjustment will stop the noise. A Professional needs to make that adjustment. As long as you don't have soot from the seams of the vent pipe or lots of black smoke leaving the chimney top outside, you may be just fine waiting.

Eventually that will turn to soot and will grow exponentially within just a few hours and you will need to shut the boiler down until those fire tubes are cleaned and the burner is serviced. Lets just hope that does not happen until the owner returns home.

epmiller · March 2

Thank you all for your comments and help. I have not been able to get to the computer since my last comment, I didn't disappear.

@EdTheHeaterMan thank you for the info on the Dynatherm boiler. The diagram of all the points of connection look just like what I see on that boiler. I've been keeping an eye on things and I have not observed any black smoke out the chimney just "steam", condensing combustion gasses. It's an external block chimney and the boiler doesn't cycle long enough to get it warm the whole way up. It also had a domestic hot water coil in it but it failed (relief valve was leaking constantly, system pressure about 35psi) about five years ago and I capped it off and put an electric water heater in for him, he thought he was going to have the boiler replaced shortly back then but it's still here.

The owner returned late this afternoon but we won't overlap when we are both home (he works ridiculous hours) but I will get to see him later this week so we'll talk then. I love learning something new, I wish I was younger, I'd get some training, tools and test equipment and add oil burners to my list of things I service.

oil boiler loud drone when firing

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