possible detonation

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jcaufield

New Member
Jan 12, 2011
3
NM
Hi All--

We have a new Harman P43, about 2 months old. We have burned about 70 bags of pellets. It has been making augur noise, mostly audible on startup. This is probably in the gearbox, because the sound is pretty far back in the stove. We called the store last week about it, and they said they would come check sometime. I clean the burn chamber pretty much daily. But this last time we had a problem when it was starting up. There was a muffled bang, loud enough to scare us some. It seemed louder than the pop you get when the augur gets caught on a pellet. By the time I made it around the corner to see, you could see smoke venting from all sides of the glass door! It was coming out on all sides, curling away in a way that told me it was high overpressure. My wife was right there, and she thinks that it flashed.

I figure that it was a detonation at startup, caused by pellet dust swirling until it ignited. So I'm emptying the hopper right now, and vacuuming the thing out. It did contain the problem, but I worry about the glass and people sitting in front of that.

The store had told me it was safe to run, but now I'm not as sure. I guess I'm going to clean it and keep people away as it starts.

Anybody else had this problem?
 
jcaufield said:
Hi All--

We have a new Harman P43, about 2 months old. We have burned about 70 bags of pellets. It has been making augur noise, mostly audible on startup. This is probably in the gearbox, because the sound is pretty far back in the stove. We called the store last week about it, and they said they would come check sometime. I clean the burn chamber pretty much daily. But this last time we had a problem when it was starting up. There was a muffled bang, loud enough to scare us some. It seemed louder than the pop you get when the augur gets caught on a pellet. By the time I made it around the corner to see, you could see smoke venting from all sides of the glass door! It was coming out on all sides, curling away in a way that told me it was high overpressure. My wife was right there, and she thinks that it flashed.

I figure that it was a detonation at startup, caused by pellet dust swirling until it ignited. So I'm emptying the hopper right now, and vacuuming the thing out. It did contain the problem, but I worry about the glass and people sitting in front of that.

The store had told me it was safe to run, but now I'm not as sure. I guess I'm going to clean it and keep people away as it starts.

Anybody else had this problem?
Click to expand...

It was more than likely gases from smoldering pellets. Tell us when and how you clean your stove.

Ignitions like that usually happen because of dirt somewhere in the system. It can be something blocking the air flow around the igniter or something blocking the air flow in the stove proper.

They are not uncommon with ash filled pellet stoves.
 
I agree 100%

Our Quad will do the Poooof thing at times if the pot has a clinker over the ignitor port.

The pellets smolder a looooooong time and then when the gases are just right, whoooomph off it goes.

There is plenty of venting so the glass is not likely to blow out, its just a little unerving is all.

Th best thing to do is a complete cleaning, including the vent system, ash baffles, ignitor port/firepot, exhaust fan and housing.

Make sure the little beast is clean and the issue should go away.

Keep us posted


Snowy
 
The guy in the video (hope it wasn't anyone here) had to stage that just for the 'show'. He probably loaded up the burnpot with a lot of extra pellets from the looks of the flame. Pretty dumb thing to do, really. Again, I hope it wasn't anyone here. ;-P
 
It was a violent ignition clean your stove not getting enough heat to the pellets fast enough open the clean out under your burn pot.
 
maglite67 said:
It was a violent ignition
Click to expand...

That's an understatement!!! %-P Look at the size of that flame after ignition! He filled the pot up far enough to cover the igniter hole so that it took a long time to ignite and built up all the extra gas. I sure hope no one runs with a flame that high!!! Either he did it on purpose or he has no clue on how to adjust the stove's feed rate. In either case, HE is the reason for insurance companies worrying about pellet stoves. The logical thing for him to do is sell the stove.
 
tjnamtiw said:
maglite67 said:
It was a violent ignition
Click to expand...

That's an understatement!!! %-P Look at the size of that flame after ignition! He filled the pot up far enough to cover the igniter hole so that it took a long time to ignite and built up all the extra gas. I sure hope no one runs with a flame that high!!! Either he did it on purpose or he has no clue on how to adjust the stove's feed rate. In either case, HE is the reason for insurance companies worrying about pellet stoves. The logical thing for him to do is sell the stove.
Click to expand...

Perhaps it was a second starting fuel dump because the first failed to light off or the burn pot had a clinker in it, the point is any (yes I do mean any) heating device that ignites its fuel (yep I got to watch an oil fired hot water heating system blow a flue vent cap off) can do that.

There are several other examples on youtube. One was after an entire years worth of burning.
 
I throw a handful of pellets in the pot before I restart it, sometimes two. This gives the same effect you describe. I do this to get the heat up faster. Been doing it for two years with no problems.
 
I just find it amazing that he JUST HAPPENED to have the camera handy. What a coincidence......... Yea, I throw a few pellets in the pot after a cleaning since inevitably the vacuuming pulls the first few pellets out of the auger.
 
Hi All--

Thanks for the many replies.

As for cleaning, we shut down daily, scrape burn pot, brush inside the burn chamber. After about 25 or so bags I empty the ash bin, open the lower panel/door to the access the fan, and also clean the passage back. (I use a shop vac and brush for this.) I think that's everything it says to do in the manual. This is my first year with the unit, so maybe I'm missing something.

Last week we started getting a grinding noise from toward the back of the unit, happening on start-up. So I went to the store, and they said they would send someone out. I said I was ready to do the after-season cleaning, to see if that would help. The store manager told me not to do anything to it-- I guess she wanted it to be diagnosed first. There was concern that it was dust in the auger, I think.

When nobody came that night, we got pretty cold, only running a back-up furnace. So I called the technician the next day and he said, yes, use it, and that he would make it out soon.

So I was ready to clean more than prescribed, but was under instructions not to. Once we had this incident I decided to clean it anyway. I did vacuum out the (empty) bin and along the auger as much as possible-- there was a lot of dust, between 1/4 and 1/2 cup I would guess. I also removed the wing nuts under the burn pot and sucked out the ash. There was some there, but the opening created by the removed cover was not completely ash-filled.

We kept people out of the room while reigniting. It worked fine.

I saw the video, but don't have sound, so I couldn't check that. Our stove had smoke curling away from the edges of the glass door, on all sides. I don't see that in the video.

I would guess the total number of bags burned since new is actually about 65, not 70 as I estimated earlier.

Thanks!
 
What happened was when you restarted the stove after cleaning out the hopper, the stove went into start up with no pellets in the auger tube. I had this explained to me once before and I could be wrong so if there are some Harman techs out there please correct me.

So, the stove goes into start up, no pellets in the tube, ESP senses no heat, dumps more pellets into burn pot and eventually you get to many pellets in the pot. The pellets smolder creating excess pyro gas, finally igniting and KA-BOOM. You probably had burning pellets going into the ash pan too?

I had the same problem, only happening after restarting after running out of pellets. The cure, refill hopper with pellets and run in test mode for a minute or 2 to fill the auger tube with pellets. A Harman tech told me this and I have never had a ka-boom since.
 
Hello Maine--

Well, I could see how an empty auger might bring about a detonation. But I emptied the hopper and cleaned *after* the detonation. So that wasn't the cause. When I started having problems, the store told me not to clean it. Then I had the detonation.

I did watch the early part of the first restart (I left the room before ignition!). I noticed there were still pellets in the auger, so that wasn't a problem this time. Maybe your shopvac is better than mine! But I will watch for that in the future.

So I am going with the theory proposed above, that the burnpot was not clean enough to light quickly. This is a bit odd, since the stove is new and we had just barely passed the 1 ton mark. (I miscaluculated before, thinking that a pallet of 40/40 pound bags was a ton, but it is only 1600 lbs. So I was counting about 10 bags high. In reality we had burned 1 pallet (40) plus 10-15, so 50-55). It seems strange that there isn't a bigger safety margin. I'm also not happy that the store told me not to do anything, and then never came, despite a bunch of calls.

Thanks again.
 
I had an issue last night with some pellets that were at the bottom of the stack and about 5 years old. Stove ran out of pellets while I was at work, I needed to clean it anyway so it worked out fine. scraped the pot, filled the hopper and vaccumed out the bottom of the stove. Ran in test mode for a minute and went to auto ignite. after about 10 miinutes it went into 4 blink status and pellets had just started going over the edge. Thought maybe the ignitor failed, long story short, scooped all the pellets out of the pot, removed the wing nuts and plate, cleaned out the chamber, put in a handfull of new ones I got on tuesday and went into auto ignite, it proceeded to run the auger until the pot was nearly overflowing again when I saw some smoke and a flame start. I had a burn pot filled to the brim with pellets and I was concerend it was going to " POP " but didn't. I think there are a bunch of factors that go into why one stove pops and other don't. vent cleanliness, stove cleanliness, combustion blower cleanliness, vent configuration, you get just the right mix of gasses and ignition and BOOM.. I am of the belief that there should never be any type of boom when lighting a pelelt stove, the blower should be evacuating any excess gasses out of the vent during auto ignition.
 
On several occasions when starting my P38 (manual start), I noticed there was flue blockage obviously due to a temperature inversion. The chamber filled with smoke causing me to worry about a flash. Each time however the flue opened and the smoke cleared almost immediately. In that situation is there a possibility of a flash and could that have occurred in this situation?
 
I am an advocate of using a smallish (1/2") paintbrush to clean the ignitor on the Harman stoves. The way that thing is mounted in there with the bracket makes it highly susceptible to ash filling in the fins on the ignitor...a couple of jabs with the brush usually knocks anything out of there.
 
jcaufield said:
Hello Maine--

Well, I could see how an empty auger might bring about a detonation. But I emptied the hopper and cleaned *after* the detonation. So that wasn't the cause. When I started having problems, the store told me not to clean it. Then I had the detonation..
Click to expand...

You refere to this as detonation. It is not detonation, it is merely ignition. Although not the ignition you expect. Detonation is far different and unlikely to occur in your pellet stove. If it did, serious damage would occur.
 
I agree, bd, this detonation thing is getting old fast. It's total BS. So you get a 'poof' once in a while. Sell your stove if that upsets you! ENOUGH!!!!!!!!!!!!!!
 
Delta-T said:
I am an advocate of using a smallish (1/2") paintbrush to clean the ignitor on the Harman stoves. The way that thing is mounted in there with the bracket makes it highly susceptible to ash filling in the fins on the ignitor...a couple of jabs with the brush usually knocks anything out of there.
Click to expand...

This.

Also, a handful of pellets in my stove after a hopper emptying can cause a fair amount of smoke, but nothing like a kaboom. Not even a pop.
 
Can someone explain to me how you can have a fire without smoke. I mean, doesn't wood change to a gas BEFORE it ignites? I mean, if I heaped my hopper with p's and struck the lighter, wouldn't go to immediate flames would it? And anyway, how much smoke do you have to have to get an explosion? Wouldn't the concentration of smoke displace the oxygen and well... cause it to smolder more.

I know once and the worst I have ever seen on my stove, the smoke built up and caught fire and the cloud was maybe four or five feet above my stack. Hardly an explosion more like a llama fart.
 
Smoke contains oxygen. Smoke doesn't displace oxygen.

"this has been a public service announcement".
 
Don't forget to check your voltage. A perfectly clean stove can have delayed ignition if the voltage is low (<117V). This situation is worse when it is really cold (like now) because the low voltage imparts less power to the ignitor and with the cold air whistling past it, less heat is transmitted to the pellets so the burn chamber fills with volatile gas (smoke) and then ignites all of a sudden.
 
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