Kaboom? Is it my boiler?

vaporvac

Hi all! It's been a while since I've posted a thread, although I read the posts everyday. I've consider that a good thing as it's meant clear sailing until very recently when I've heard a kaboom about three times on separate days in my basement. I can only assume it has something to do with either my boiler or WH, but the noise didn't seem to be from the WH.
As a refresher, I have twinned SF TR50s with probe LWCOs on my Trane Vaporvacuum system., so no pilot or bottom burners. When I ran down to check on the boilers they were almost at the end of their cycle when they reach 12-16oz. they shut off within a minute or two. I'm stymied, as it sounds like the delayed ignition explosion I had on my old atmopheric when the burners were rusted, although to a much lesser degree. but clearly they weren't at the beginning of their cycle. I'm wondering if there's something wrong with the LWCO which will often shut off a boiler for a very short while as the condensate returns. (I have a very long mains.) Perhaps there's delayed ignition then whith the gas valve opening too soon. Can a tech check for that? I've shut off the boilers and have an appointment for tomorrow AM with the great tech I found a couple of years ago, but I'd like to offer some possibilities as I'm sure it won't happen while he's here.
Thoughts anyone?

Fred

We had a similar post a few weeks ago, @vaporvac . The homeowner was able to focus a camera on her boiler and captured the event. If you can do that it may explain a lot.
Is there just one particular boiler running when this happens? Narrowing down the likely boiler will help the tech a lot. Have you watched either boiler enough, through a full heating cycle to know how often the Vaporstat may shut the boiler down on pressure and within seconds of firing back up the LWCO shuts it down on low water. Possibly not enough delay between start and stops to completely shut the gas valve??? Just thinking out loud.

vaporvac

Hi @Fred ! I read that post and though that's exactly what my old boiler must have looked like when the burners rusted up. Replacing them fixed the problem, but the wet-based boilers have the burner in the middle of the firebox and hopefully, my boilers aren't rusted out yet!!! I'll have to find that thread again and see what her issue was. I don't have anything to video them.

I honestly don't know if this is one or both of the boilers as both should be running when this happens which is only three times. However, once was enough. I haven't been running toggling the boilers much this year. . Last year I only ran one (1) boiler after reaching temp. because it was colder and a single boiler could easily maintain. I wasn't sure if that would work with such intermittent firing due to the fairly warm temps we've had.

I have spent a lot of time watching through the cycle...it doesn't always shut off on LW each cycle and if it does it's only once per cycle and then it starts up really quickly as the condensate pours back. I wish I'd noted when in the cycle it would shut off, but now I'm a bit afraid to turn them back on. They never really shut off on pressure. Both my Vstat (one old/one new) failed so it just runs until it makes temp never reaching over 140z. If it shuts off on LW, then it only goes to a couple of oz. upon re-fire.Your idea could be the case, except the power burners have a purge cycle before they fire.

Paul48

I'd buy the cheapest thing I could find to video them. An intermittent problem like that could drive you crazy. It may be the only way to confirm exactly what the problem is.

JUGHNE

This most likely has nothing to do with your noise.

Are both boilers sharing a common return?
If so then there are 2 boilers water capacity available to boil away and you still go off on LW?

vaporvac

I'm going to try to find something tomorrow to record it, if we can't get to the bottom of it. 's @JUGHNE, do you mean the explosion has nothing to do with my boiler?
Yes, both boilers share a common return. The boilers together equal the necessary edr, but once hot one will keep temp. They are not redundant in the sense that each boiler is 100% of the EDR. The water is approx. the same as if I had a single boiler for my 150' main. It doesn't always go off on LW. Usually it's only if it hasn't run for a while. SFin and others on here said I may need a condensate tank, but it's generally OK. I don't know if it's related to the noise.

JUGHNE

What I meant was that my question concerning condensate return would have nothing to do with your kaboom.

Do your burners have a post purge feature?
A hot combustion chamber could be lighting stray gas fumes with a single pop.

ttekushan_3

Purely conjecture, but I would pay close attention to the ignition rod that I believe those burners use. Weak spark takes longer to light. Any worse and it might lock out on ignition failure.

Though this usually results in a Whump light off rather than an explosion. @JUGHNE has a good point about the purge cycle. That was one of the few times I had an explosion. Very old burner with no purge functions. Very memorable.

Which brings up something else. Any water leakage in a combustion chamber can cause a less-than-graceful start. But let's not panic over that possibility yet.

First get the burners cleaned and set up with an analyzer. With special attention to the pilot burner ignition.

EBEBRATT-Ed

Usually with delayed ignition you will find some evidence on top of the boiler, or on the floor. Soot or dust blown out of the flue pipe, cleanout covers etc. Even in a well sealed boiler there is probably some evidence of delayed ignition

vaporvac

duplicate post. How do I erase this?

vaporvac

Can we say frustrating? So far no kaboom, of course, and no evidence of soot. We've eliminated the LWCO as a factor, since when we induced that the pressure dropped so quickly there's no way it could have reached the 1lb. I observed at the boiler after each boom. The events were always at the end of a cycle. The probes work perfectly. Start up on the burners is clean also. Combustion numbers are good with EFF ~ 85%. It was a little over 87% last year.
He's checking out the firebox, so fingers X'ed. Firebox perfect and intact. He cleaned everything, but said it looked normal. Hmmm.
Guess I'll need to record it. Anyone remember the thread with the video mentioned above? I'm looking for suggestions on the cheapest recording device. thank you again.

Abracadabra

basic IP camera that also records audio or if you have a laptop a basic USB camera with some shareware to record with audio trigger

ChrisJ

Why not shut down the boiler(s) and restart them a few times while standing there?

If they fire right up reliably 10 times or so, I'd start doubting a problem.

vaporvac

Thank you @ChrisJ . We did do that a few times. If someone else hadn't heard and felt the thunk with me, I'd have been doubting myself. It is possible it's some random tree limb fall down the back forty or something elsewhere in the neighborhood. I'd prefer that, but figured 3x can't be a coincidence. Oh well. I needed the boiler burners, etc. cleaned and checked out anyway.
It's just odd that it's at the end of a cycle when the burners must have been full on. There's absolutely no whiff of gas either. I will check all the joints with soapy water, just cuz better safe than sorry.

hvacfreak2

If this doesn't seem to be burner related is it possible that it could be water hammer ? I know that this is usually a shrill sound but if it happens down low in the piping system maybe it could be heard as a " thump " ? At the end of the heating cycle it could be due to a Hartford loop piping issue( B dimension on 2 pipe , my thought on this may be wrong ) ? Someone also mentioned a sub speaker on a home entertainment sound system in another thread recently , I hope he got paid figuring that one out , lol.

Fred

Do you have a hot water loop on the boiler(s)? Is the thump a pump that may be acting differently than it did? Temp high enough to make steam in that loop?

vaporvac

Well, I thought I could close this one out thinking the burner cleaning had fixed whatever problem there was, or else it was tree fall, but NOoo! I heard another boom just now and it's definitely from the boiler area right before the pressure reaches its high of 1lb. and shuts off on temp per its usual pattern. There are no obvious signs of disturbance either.
@Fred , I don't have a HWLoop, but good thought. This definitely isn't a water hammer sound as I hand that bad before the new boilers or least it's not like what I experienced before which was like a clanging. @hvacfreak2, I'm interested in the Hartford Loop as the culprit. I think you may be on to something. Mine is at the minimum 2" below the water line. What happens if the water drops below the 2"? The strange thing is I've had these running for two full seasons and this is new just within the past few weeks.
I guess I need that camera.
I really do not need this right now as I may need to be out of town for while1The tech had no idea what it could be as everything burner related checked out fine.

BobC

Try increasing the water level by one inch and see if things change.

Bob

vaporvac

Thank you @BobC . I just did that and raised the temp 1 deg and it was fine, but it didn't reach 1 lb. Do you think there's any advantage to running just one boiler? It will still heat the house so that's not a worry.

BobC

Did the noise occur before on just the single boiler?

Bob

vaporvac

No. Only when I had them both on. No problem the past cycle after raising water level and temp. when running both.

BobC

I remember looking at the pics of your twinned boilers back when you were putting it together, am I right in saying the water levels track each other?

I'd just run them in the normal mode and see what happens.

Bob

vaporvac

Yes @BobC , the water levels track each other. Do you have any thoughts on the Hartford Loop B dimension causing the problem?

ChrisJ

If one boiler heats the house fine why use two at all?

BobC

My only thought is if the water level drops too close to the loop it could be the cause of the boom, but then I could be wrong.

Bob

Fred

Does the boom sound like a combustion issue or hammer? At the end of a heating cycle, it almost sounds like the a little gas is escaping the gas valve after the burner shuts off and igniting on heat from the hot surfaces. Is it the same boiler each time it happens?

vaporvac

@ChrisJ , I need both if coming if coming back from a set-back or if the pipes are cold as they often are since we've been so warm. Once they're warm, one is sufficient.
@BobC , will a Hartford Loop cause a boom? @Fred, I have never been in the room when this happens as it's very random, so I don't know which boiler is the culprit, or even if it's the boilers themselves. I should note that the "boom" happens DURING the firing cycle. It shuts off soon AFTER, so perhaps that negates it being escaping gas? It is at this point that the water level is the lowest.

ChrisJ

vaporvac said:@ChrisJ , I need both if coming if coming back from a set-back or if the pipes are cold as they often are since we've been so warm. Once they're warm, one is sufficient.
@BobC , will a Hartford Loop cause a boom? @Fred, I have never been in the room when this happens as it's very random, so I don't know which boiler is the culprit, or even if it's the boilers themselves. I should note that the "boom" happens DURING the firing cycle. It shuts off soon AFTER, so perhaps that negates it being escaping gas? It is at this point that the water level is the lowest.


Have you actually tried with one?

neilc

are both boilers shutting off together, or staged?
if staged could the still firing boiler, and did you say low water issue, be sending a slug or woosh to the boiler that is off?
or even if shutting down together, if one boiler cools just a bit faster, and vacs a bit , , , slug woosh ?

vaporvac

@ChrisJ , I often fire just one, but not recently since the weather is so crazy, it can be hours before they re-fire. I will try with one tomorrow. I've shut them off for the night since it's very warm in the house. Just trying to trouble shoot. Thank you everyone. Keep the suggestions coming.

vaporvac

@neilc , I haven't been staging the boilers so they shut off together. The boom happens while both are FIRING and the pressure is ~ 1lb.

Fred

Do they both shut off at exactly the same time? Is it possible that one shuts off just a tad before the other and the one that shuts down last get a surge of gas as a result of an increase in pressure?

neilc

I'm sticking with my slug woosh theoreum,
especially that you may have corrected it by raising the water level that inch,
keeping a water seal between the 2 boilers,
wondering if it's something to do with the lead lag BTU differential

vaporvac

@Fred, they always shut down at the same time. @neilc, last year the boilers were readjusted, so the btu difference is small. Some people purposefully design their twins to have differing BTUs.
I have a vaporvacuum system, so I always have vacuum, but it definitely isn't immediate. It's a gradual fall into vacuum.
I'm trying to understand the slug shoosh theorem as it happens while they are firing. Hmmmm.

Jamie Hall

I'm glad to see you back on the Wall! Always fun.

On this kaboom. Can you describe it a little further? You know what water hammer sounds like. Is it like that, at least sort of? And you know what expansion sounds like.

But... Is there, somewhere, a sheet metal panel which has come slightly loose or gotten slightly warped? Back in a previous life, when I did sound effects for theatres, I made quite convincing booms and thunder and the like with a big, almost flat but not quite, sheet metal panel. The resulting sound is more drawn out than water hammer, and lower frequency -- indeed, like a boom. If it is a sheet metal panel, it could be quite random in timing, depending on exactly the right temperatures. Boiler enclosure? Might not even be right at the boiler.

vaporvac

Hi @Jamie Hall. I'm always reading posts, just not posting or commenting if I'm on my Kindle. It's too hard to post from that.
: )
When I had hammer, I could hear it up through the house. It's like a clanging. This noise is more like an explosion. Imagine a big tree limb falling next to your house. I'd be afraid to actually be in the basement when it happens. It's one sound. quick and loud. I'll take a look at the panels tomorrow. It's the sort of sound that makes one run to the basement to see what happened.

ChrisJ

Thermal expansion causing main to shift and pop against hanger?

Jamie Hall

You'd be surprised how much of a boom you can make with a sheet metal panel suddenly flexing... or maybe @ChrisJ 's idea.