# Update: Harman Accentra keeps shutting down with the same error code: “Incomplete Combustion”



## vferdman (Dec 29, 2009)

Hello, everyone. Hope everyone had great holidays in the past few days.

Here is an update on my Harman Accentra 2 problem. To recap, I posted a few weeks ago with a problem of a 6 blink shut-down on my Accentra. I got the stove used a few months ago and it was installed in my house by a professional Harman-trained installer. It is in the corner and has a 90 degree elbow, 3 feet up, 90 degree elbow, 3 feet out through the wall for venting. It uses outside air for combustion intake via a special Harman thimble that combines the intake and vent pipes into one thimble. The vent pipe is 4". The stove kept shutting down with 6 blink error code when the demand for heat was low, but would crank for days on end during high demand periods. So far I have done the following at the suggestions of people in this forum.

1. Thoroughly cleaned the stove several times

2. Replaced the exhaust temperature sensor (ESP)

3. Tried adjusting low draft speed from one extreme to the other

4. Pulled the auger and re-sealed its bearing assembly to the feeder weldment

5. Emptied the hopper and re-sealed the seams in the hopper and the interface between the hopper and the feeder weldment

6. Made sure the intake back draft flapper isn't sticking

7. Always make sure there is no pellet bridge (that would not make for a consistent problem anyway, but still...)

After all that the stove still shuts down with a 6 blink error code when the demand is low. By that I mean the outside temperature getting into say, high 40's and the room temperature on the stove set at 65 degrees. This has happened int he last couple of days. Now that it's well below freezing again, the stove is cranking.

So, I am still at square one and am still looking for suggestions.

Thanks!


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## bobforsaken (Dec 29, 2009)

I think I remember you posting this issue.  Did you ever remove the feed to outside air and just let it use inside air?   I'm not familiar with the thimble you describe.  I'm assuming its something that pulls outside air accross the exhaust in order to heat.  If it is leaking, maybe its getting O2 Staved.


Also, when the stove burns out, does it have a burn pot full of pellets or is the burn pot empty?


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## SmokeyTheBear (Dec 29, 2009)

Vladimir,

Could you provide some pictures of your outside vent set up and tell us where in the prevailing wind pattern it is?


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## THE ROOSTER (Dec 29, 2009)

It sounds to me like the stove is shutting down completely and then not starting back up... If you are running in "Room Temp" try switching it to "Stove Temp" then running it as low as it will go and see what happens...


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## Dougsey (Dec 29, 2009)

Try disconnecting the OAK.

I'm thinking some weird back draft that's tripping the vacuum sensor (although I'm not positive that would throw a 6 blink error).


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## SmokeyTheBear (Dec 29, 2009)

Dougsey said:
			
		

> Try disconnecting the OAK.
> 
> I'm thinking some weird back draft that's tripping the vacuum sensor (although I'm not positive that would throw a 6 blink error).



Loss of vacuum does cause a 6 blink error, that is the reason all of the sealing etc ... was done.


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## rickwa (Dec 29, 2009)

I still think you neeed to buy 3-4 bags of a different brand of pellets to rule fuel out.  I know you said you have a few tons of what you have in the garage but when you have a never ending problem you need to start the process of elimination until you come to the problem.  there is most likely one thing wrong that is causing all your problems but so far it has been very elusive.  I think fuel is about the only thing you havent tried.


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## investor7952 (Dec 30, 2009)

vferdman said:
			
		

> Hello, everyone. Hope everyone had great holidays in the past few days.
> 
> Here is an update on my Harman Accentra 2 problem. To recap, I posted a few weeks ago with a problem of a 6 blink shut-down on my Accentra. I got the stove used a few months ago and it was installed in my house by a professional Harman-trained installer. It is in the corner and has a 90 degree elbow, 3 feet up, 90 degree elbow, 3 feet out through the wall for venting. It uses outside air for combustion intake via a special Harman thimble that combines the intake and vent pipes into one thimble. The vent pipe is 4". The stove kept shutting down with 6 blink error code when the demand for heat was low, but would crank for days on end during high demand periods. So far I have done the following at the suggestions of people in this forum.
> 
> ...




I had this error when stove was installed. It will run ok in stove temp but not room always a 6 blink. Turned out the room temp sensor was pinch and went bad. Put a new one on never had the problem again


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## GVA (Dec 30, 2009)

As I said in the other post......
"_There are several things that cause the 6 blink
Board
ESP
no pellets
The stove actually is sensing poor combustion.

ESP has been changed
that leaves the board or no pellets…...Usually

reason for no pellets

Auger motor is bad
bridge in the hopper
bad combustion blower
bad vacuum switch
plugged exhaust
leak in the system
or any combo of the above

we just need to break down all the above
if you’re vac switch opens while the combustion blower is running then 
you have a weak draft caused by a failing comb blower, plugged exhaust, leak somewhere in the negative pressure fire box etc…....

It’s possible that you did get a bad ESP replacement….Though doubtfull

If it was a small vacuum leak then turning the draft pot all the way down would trip the stove more frequently I would suspect.

I think that you may have a bit more natural draft right now due to the cold temps that have arrived in Mass, (though i’ve been wrong before)  

I think the vac switch IS opening for some reason though"_


The stove is shutting down when you're comb blower speed is kicked down to low draft, this is why I think the vac switch is opening and shutting down the stove..
I would look at the comb blower/venting/vac switch/vac tube etc..........Quite possibly a weak combustion blower is the whole problem.....

Stepping on my soapbox here
DRAFT TEST...
Stepping off soapbox now


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## vferdman (Dec 30, 2009)

Thanks, everyone for more suggestions and comments. It has now gotten very cold outside (single digits) and that in the past made the condition go away. So I am now not able to test the various suggestions. I did put the stove in "stove temp" mode and it has been running all night. I am not sure that proves anything, though as it is very cold and the demand is high. The problem usually occurs during low demand periods. I will post pictures of the thimble later, but let me just say that it is a simple device that combines two openings into one fixture, that's all. The intake and exhaust are in no way combined or aggregated. I have tried running with outside air disconnected from the stove and that made no difference. I may try a room temperature sensor, but I am already out $50 on the ESP which I did not need, so I am a bit gun shy about spending more on trial and error. I may try and buzz the room temperature sensor wire for continuity, but other than that I am not sure what could go wrong with it. It is practically indestructible thermistor, isn't it? anyway, I will try most things within reason, but really don't want to throw replacement parts at the problem without some justification.

Thanks!


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## investor7952 (Dec 30, 2009)

vferdman said:
			
		

> Thanks, everyone for more suggestions and comments. It has now gotten very cold outside (single digits) and that in the past made the condition go away. So I am now not able to test the various suggestions. I did put the stove in "stove temp" mode and it has been running all night. I am not sure that proves anything, though as it is very cold and the demand is high. The problem usually occurs during low demand periods. I will post pictures of the thimble later, but let me just say that it is a simple device that combines two openings into one fixture, that's all. The intake and exhaust are in no way combined or aggregated. I have tried running with outside air disconnected from the stove and that made no difference. I may try a room temperature sensor, but I am already out $50 on the ESP which I did not need, so I am a bit gun shy about spending more on trial and error. I may try and buzz the room temperature sensor wire for continuity, but other than that I am not sure what could go wrong with it. It is practically indestructible thermistor, isn't it? anyway, I will try most things within reason, but really don't want to throw replacement parts at the problem without some justification.
> 
> Thanks!



Trust me its the room sensor it is defective. I have gone through the same a yr ago. Its not the esp its the room sensor. This is why you are running flawless in stove mode because you are by passing the room sensor. Replace the room sensor and your problem is fixed.


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## Bigjim13 (Dec 30, 2009)

investor7952 said:
			
		

> vferdman said:
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One thing to add to this, i had the same problem with my room sensing probe and got a new one from the dealer.  I installed it and was still getting the error code.  I had the service tech come out to look at it and it turned out that the computer was picking up the sensor but the sensor was reading that it was 99* in the room where the stove is.  He reset the comp and (knock on wood) haven't had a prob since.


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## vferdman (Dec 30, 2009)

investor7952 said:
			
		

> Trust me its the room sensor it is defective. I have gone through the same a yr ago. Its not the esp its the room sensor. This is why you are running flawless in stove mode because you are by passing the room sensor. Replace the room sensor and your problem is fixed.



Well, I just got the 6 blink shut down in the stove temp mode. Actually I got two shut downs in a row on stove temp. It got a little warmer (around 25-30 outside) and I got a shut down. Been running in stove temp since last night. Ran through the night, but the night was very cold. During the day it got warmer and I got a shut down. That pretty much eliminates the room temperature probe.


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## vferdman (Dec 30, 2009)

Bigjim13 said:
			
		

> One thing to add to this, i had the same problem with my room sensing probe and got a new one from the dealer.  I installed it and was still getting the error code.  I had the service tech come out to look at it and it turned out that the computer was picking up the sensor but the sensor was reading that it was 99* in the room where the stove is.  He reset the comp and (knock on wood) haven't had a prob since.



Now what's that you say about Harman tech resetting the computer? I wonder if that's what I need done. It just seems like a software glitch (I am biased as I used to develop low level software like this). Is there any information on how to reset the computer? I see some dip switches on the PCB, and there is a small header also. So there is a way to connect some instrumentation to this thing.

Also, did you end up keeping the new room temp sensor or did you go back to the old one with everything working fine after the reset? This is very interesting.


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## investor7952 (Dec 30, 2009)

A tech should come out with a computer hook up just like when a mechanic plugs a car into a program and it will trouble shoot.


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## Bigjim13 (Dec 31, 2009)

vferdman said:
			
		

> Bigjim13 said:
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After I made about 6 calls to the dealer and got them to believe that I wasn't an idiot who didn't know how to troubleshoot or just plain didn't clean my stove they had a service tech come out to see what the deal was.  On my stove, a P61A, on the control board there is a plug in (looks like a USB port) that the tech plugged in his computer to.  He could see right away that the room sensor was reading that it was 99* in the room with the stove.  He reset it and that was it, here for about 20 min tops.  Unfortunately I don't know if you can get the equipment to plug into the stove or the diagnostic software if there is such a thing.  

I didn't end up keeping the old probe, they asked me to bring it to the shop so they could look at it before giving me a new one.  I assume they either threw it away of sent it back to Harman to get credit for it.  I imagine if you call your closest dealer they could do something similar and at least point you in a direction to get this fixed.

I downloaded the manual for the accentra and frankly not much help there (not surprising mine isn't all that helpful either).  Anyway the port I was talking about is for a "special DDM monitor supplied exclusively to Harman dealers" so I think you're out of luck there.


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## maglite67 (Dec 31, 2009)

The DDM only tells you what the control board is reading and not any special info on how to fix it.  I would guess room sensor or your feed rate is to low another problem could be your glass gasket but then you would have a burn problem.  Feed rate is not a method to save fuel it's a way to keep your burn pot from overfilling from pellet to pellet.  Too little feed not high enough temps and the stove goes out on 6 blinks.


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## Lousyweather (Dec 31, 2009)

maglite67 said:
			
		

> The DDM only tells you what the control board is reading and not any special info on how to fix it.  I would guess room sensor or your feed rate is to low another problem could be your glass gasket but then you would have a burn problem.  Feed rate is not a method to save fuel it's a way to keep your burn pot from overfilling from pellet to pellet.  Too little feed not high enough temps and the stove goes out on 6 blinks.



The DDM tells you what the dip switch settings are, which board it is, the voltage to the combustion blower, what the feeder setting is, if the ignitor is on or off, the room temp probe temperature being sensed, what the temp setting is, and the ESP probe temperature being sensed, but yes, its only a helpful diagnostic....it does NOT tell you what to do, and nor can the circuitboard be "reset', so to speak. Also, a draft reading is very nice to have as well........and he does have a burn problem...thats what the 6 blink indicates......


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## Bigjim13 (Dec 31, 2009)

Lousyweather said:
			
		

> maglite67 said:
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So if the circuitboard can't be reset what would the Harman tech have done in my situation where the room probe was reading that my room was 99*?


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## Lousyweather (Dec 31, 2009)

no, it CANT be reset.......if I plugged my DDM and in, and read the room probe to be reading 99 degrees in a cold room, I'd either think the owner had the probe somewhere warm, OR the probe was defective......and replace the probe...


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## SmokeyTheBear (Dec 31, 2009)

Lousyweather said:
			
		

> no, it CANT be reset.......if I plugged my DDM and in, and read the room probe to be reading 99 degrees in a cold room, I'd either think the owner had the probe somewhere warm, OR the probe was defective......and replace the probe...



If the room probe were not connected what would the temperature read ?


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## Lousyweather (Dec 31, 2009)

you would get a status light error if in room temp mode, but if the stove was running in stove temp, you would get no error at all....


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## Bigjim13 (Dec 31, 2009)

Lousyweather said:
			
		

> you would get a status light error if in room temp mode, but if the stove was running in stove temp, you would get no error at all....



The stove ran perfectly fine in stove temp, the only issued was in room temp.


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## SmokeyTheBear (Dec 31, 2009)

Lousyweather said:
			
		

> you would get a status light error if in room temp mode, but if the stove was running in stove temp, you would get no error at all....



Ok, was wondering if it would treat the missing sensor as having reported a temperature that was at one of it's temperature extremes, funny thing about software, if it is snafued you frequently get strange presentations.   Vladimir being a software hardware interface person understands where I'm heading with this.

I'm afraid that I must also admit that I've rolled several hundreds of thousands of lines of code, some of which was playing with signal decoding and presentation, and a lot of which was good ole bread and butter large commercial systems, along with more than a little operating system bit twiddling.


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## Lousyweather (Dec 31, 2009)

dating myself here, but I did Fortran programming years ago! ack! Gosh, Im old!

no, if the board is running in stove mode, the room probe can be non-existant, but, in Room Temp mode, if the probe is faulty or non-existant, you should get a "4 blink" error......switching to Stove mode effectively ignores the presence of the room probe, or lack thereof.


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## vferdman (Dec 31, 2009)

Wow! This is really generating lots of discussion. I like it. Well, I don't like having a malfunctioning stove, but I do like having so many bright minds at work on this problem. All suggestions and thoughts are very good, but so far we are coming up empty. The feed rate is set at 5, but I did try setting it at 6, which is the maximum possible. No joy. The room temperature probe is most likely fine as it is nothing more than a thermister on a long wire. I tried unplugging it and I get a 4 blink error with it unplugged in room temperature mode. To recap, I did try running in stove temp mode and still got a 6 blink shut down, so I think we can let go of the room temp probe for the moment. I would love to get a hold of the diagnostic tool that reads all the signals the control board has to work with. That would be JUST the ticket for me. I have spent much time professionally troubleshooting complex signal processing software (on Voice over IP phones for example) and would be very comfortable using such a device to troubleshoot. I just feel we are flying blind here without knowing what exactly sets the 6 blink code. Seems like there are several paths to it (logically speaking). One is when the exhaust temp is too low for a given feed rate (I am guessing here, but I think it's a good guess), the other is perhaps when the room temperature does not increase when the exhaust temperature reads high enough (???). I am sure there are other possibilities. If I saw the data I would be able to deduce a lot more than I can now. Anyway, this is neither here nor there as no one has access to these diagnostic tools, it seems, except the Harman techs. So, we'll have to do it the hard way, I guess. Here are some more observations that I have not yet posted.

The stove seems to run fine until there is a lot of carbon build-up in the pot. I scrape the build-up, but not every day. Maybe I should do it every day. 

In low heat regime there seems to be more build-up created. This may be my imagination, though. I do get a carbon ridge just around the lowest holes in the pot. The ones around the igniter. I took the igniter off and poked the holes out to make sure everything was clean. I noticed that the row of holes near the igniter does not go all the way across the pot. There are just holes half way across. Only to where the igniter is. I assume those are the special igniter holes, though they do participate in normal combustion. I am thinking that they get clogged up easily, perhaps. Just a thought. Maybe could use some more holes? I am not against drilling the burn pot.

I notice that the glass has a two dark soot spots way on the bottom left. You know where the air wash holes are. Well the two leftmost air wash holes seem to not be effective and I get two spots the size of thumb prints. Can this mean a leaky glass seal? Doesn't seem that way, but what do I know?

I get some smoke in the hopper when I open it to refill the pellets. I pulled the auger before and noticed nothing unusual about the auger. The tip of it was pretty dark and sooty and even a bit sticky, but it seems normal as it is right there in the fire. Not sure if the smoke in the hopper is a big deal. I think it's pretty normal seeing how the hopper is right above the burn pot and there is an opening from the burn pot (via auger and the flat steel plate above it that moves back and forth as the auger turns). So I am not sure this of any concern. Thoughts?

Next thing on my mind is the combustion motor. Any way to test it? It may be intermittently shorting out in the windings and becoming weak SOMETIMES, but not always. The stove seems to be from 2006, but I am not sure, it may be a little older than that. It is not super old, though. Thoughts on the combustion motor?

Thanks again!

P.S. Fortran was my second programming language, first being Basic. Used Fortran while working at a power utility company in Massachusetts (New England Electric in those days, now National Grid). So, no worries dating oneself


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## SmokeyTheBear (Dec 31, 2009)

The only time when I had smoke in my hopper was when there was a spot where the feed chute met the auger tube that wasn't sealed.  The leak there effectively bypassed the sharp bend allowing a bit of a draft to take place.  If your hopper lid doesn't seal this could result in a partial loss of "vacuum".  I wonder just how sensitive that vacuum switch is and what kind of draft you have at low burn (back to that good old mag. again).


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## vferdman (Dec 31, 2009)

SmokeyTheBear said:
			
		

> The only time when I had smoke in my hopper was when there was a spot where the feed chute met the auger tube that wasn't sealed.  The leak there effectively bypassed the sharp bend allowing a bit of a draft to take place.  If your hopper lid doesn't seal this could result in a partial loss of "vacuum".  I wonder just how sensitive that vacuum switch is and what kind of draft you have at low burn (back to that good old mag. again).



The hopper lid has a very healthy looking seal and I never get any problems where the auger motor does not turn (which would be due to the vacuum switch opening due to loss of vacuum). When the 6 blink error occurs I usually restart and things get going again. It may be that the vacuum switch opens temporarily and I am just not catching it in the act. That certainly is a possibility as I have never been present at the moment of the code getting thrown.

Again, I have no access to diagnostic tools for this stove, which is unfortunate. I may go ahead and hook up my Fluke 87 to the vacuum switch as was suggested earlier and see if I can catch the switch opening the circuit. It's worth a shot at this point as I have absolutely no other facts to support any problem.

As I said before, I did seal the hopper-to-auger tube interface (maybe not well enough?) and the auger assembly to the feeder weldment (again, did I not do a thorough job of it? It's possible).

So, is the smoke in the hopper a symptom or is it on the normal side of things?


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## investor7952 (Dec 31, 2009)

REPLACE THE ROOM TEMP SENSOR IF ITS NOT THAT i WILL MAIL YOU A CHECK FOR THE PART.


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## vferdman (Dec 31, 2009)

investor7952 said:
			
		

> REPLACE THE ROOM TEMP SENSOR IF ITS NOT THAT i WILL MAIL YOU A CHECK FOR THE PART.



I really appreciate your offer, but the stove shuts down in Stove Temp mode as well, so how can the room temp sensor be a culprit?


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## SmokeyTheBear (Dec 31, 2009)

vferdman said:
			
		

> SmokeyTheBear said:
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There should be no smoke in the hopper at least not on my stove, I wouldn't think so on your stove either but I can't say that for certain.


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## Delta-T (Dec 31, 2009)

smoke in hopper is not normal. You may be getting the "gummy stove" (search, I know there are threads here discussing).


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## GVA (Jan 1, 2010)

Turn the draft pot all the way ccw
and see if the stove shuts down more frequently.


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## vferdman (Jan 2, 2010)

Well, now that I have read a bunch of posts on the topic of "Gummy stove" and "Smoke in the hopper" I have decided that my stove may be one of the unlucky ones. Here are the pictures of the slide plate, auger and empty hopper with the brown ring formed by the smoke. Please let me know if this is a gummy stove. Sure looks that way to me. Anyway, while the auger was out I cleaned out as much as I could the auger housing which had a lot of gummed up fines balls in it. I also found another place in the hopper that could use some sealant and sealed that. I also noticed that the feeder side cover for fines and side plate access had the foam seal damage around the hole for the threaded stud. I happen to have some of that type of foam on hand and was able to cut out a square of the old stuff and glue on a piece of new stuff and carefully punch a hole in it for the stud. I re-assembled everything and disconnected the outside air before firing her up. I read that outside air sometimes causes smoke in the hopper. I think the smoke in the hopper makes things go bad eventually. Gummed up fines create resistance for pellets, which could starve the stove for fuel and throw a 6 blink error. So far the pellets are down about half way in the hopper and no smoke and no shut down over night (but I ran it at 70 degrees on room temp). I now turned the temperature setting down to 66 degrees and the stove shut itself off (without error, simply because there was no demand) and restarted later without issue. Will see how things hold up.


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## SmokeyTheBear (Jan 2, 2010)

Vladimir,

Did they say what the mechanism was that caused smoke in the hopper with outside air?   

I could see that being the case if the hopper became the highest non constricted air path out of the stove.


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## Lousyweather (Jan 2, 2010)

congrats, Vlad, youve got a "gummy" stove! The slide plate actually sticks in place, causing 6 blinks galore! And it only gets worse, not better! We have cleaned these to some degree of success, but its a pretty big job....the sticky stuff is water soluble, and you can remove the feeder weldment and soak it, and clean it the rest of the way with sundry brushes, etc. Also, maybe ought to think about adding the shrouded-in-secrecy bypass tube......we've worked on several of these....well, maybe more than several, about 20 or so....and the ones with the bypass tubes installed are still running to this day! Odd too, that any new stoves produced already have this bypass tube.....coincedence? I think not!


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## cac4 (Jan 2, 2010)

Whats the deal w/ that bypass tube, anyway?  I remember reading some posts about it a while back...but never understood exactly what is being bypassed, or how it works.

From the pics posted, it seems that I do have one of these on my stove.  It was manufactured late '06...


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## charles u farley (Jan 3, 2010)

I believe it allows a pressure balance so there is no stray pressure carrying smoke and gummy heated fuel vapor escaping past the pellets in the auger.
The hopper lid seal actually makes the hopper be just a slightly negative pressure area as air has to come from somewhere to replace the pellets as they fall out.  Without the bypass tube the air to fill the hopper comes from the auger tube, carrying smoke with it.
Just my hypothesis anyway.


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## vferdman (Jan 3, 2010)

SmokeyTheBear said:
			
		

> Vladimir,
> 
> Did they say what the mechanism was that caused smoke in the hopper with outside air?
> 
> I could see that being the case if the hopper became the highest non constricted air path out of the stove.



I am not sure what the mechanism is for getting smoke into the hopper. Others have had some ideas that make sense. This is not something that happens a lot, apparently, but enough so Harman changed the design of the feeder in 2007 to include an air port. I think this condition may occur depending conditions the stove is in as well as the individual stove itself. I have read that damp basements plus outside combustion air can result in smoke in hopper and consequently a gummy stove.


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## vferdman (Jan 3, 2010)

The stove has been running great since I cleaned the feeder after the most recent auger removal. I will be doing a thorough cleaning and possibly the modification to eliminate smoke backing up into hopper later, but I just wanted to update everyone on the status. So, I pulled the auger yesterday and cleaned out some gummy crap from the feeder. I also scraped the slide plate clean of the sticky junk (see pics a few posts earlier). I put everything back together and decided to NOT hook up the outside air. Well, this afternoon the stove almost ran out of pellets and no smoke in the hopper. So, I added about a quarter bag of pellets and reconnected the outside air. A few hours later the hopper was full of smoke. So, there you go. Outside air = smoke in hopper. No outside air = no smoke in hopper. I would much prefer the outside air intake, but I now understand that smoke in hopper leads to gummy stove and all sorts of problems. So, I will probably attempt the mod, which is described in a pdf file I got from very helpful members here. I need to wait for some more guidance, but I am ready to proceed. I also wonder why the outside air has this effect. Anyone has a clue? More resistance in the air flow circuit?


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## Saber (Jan 4, 2010)

I would be very interested in that PDF file also .


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## rickwa (Jan 4, 2010)

After seeing the pics ,you need the updated feeder installed that includes air tube


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## vferdman (Jan 5, 2010)

rickwa said:
			
		

> After seeing the pics ,you need the updated feeder installed that includes air tube



What about doing the mod myself? This is what I am going to do, I think. My burn pot does not have the 5 holes near the auger, so I should be ok to just add the bypass tube and clean the feeder, right?


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## Delta-T (Jan 5, 2010)

It is my belief that the cold intake air causes the gases that are being pulled toward the hopper (static negative pressure of hopper overcoming active negative pressure of combustion chamber) to condense and form the gummy material. I've seen gummy feeder on non-OAK setups, but far more prevailent on OAK setups. 

And yes, add air tube and clean feeder, that'll do.


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## vferdman (Jan 5, 2010)

Delta-T said:
			
		

> It is my belief that the cold intake air causes the gases that are being pulled toward the hopper (static negative pressure of hopper overcoming active negative pressure of combustion chamber) to condense and form the gummy material. I've seen gummy feeder on non-OAK setups, but far more prevailent on OAK setups.
> 
> And yes, add air tube and clean feeder, that'll do.



Sounds reasonable. I found very strong relationship between outside air and smoke in hopper. Question is: is outside air better than inside air? I realize that it is probably more efficient since we are not burning up the air we are working to heat, but other than a little efficiency loss is there a reason to use outside air? Harman installation manual changes vent pipe clearance requirements to the nearest opening (like a window or door) from 4 feet with no outside air to 1.5 feet with outside air. WHY?

Anyway, I used the special Harman thimble that has air intake as well as vent opening in it. The intake comes out of the wall just above the vent pipe. Pretty simple. It was a very expensive part (about $150 or something), but I had little choice as the stove is in the basement and first 3 feet of wall is concrete foundation.

Thanks for the info! Learning a lot as I go along.


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## SmokeyTheBear (Jan 5, 2010)

There is also a slightly higher oxygen level in the outside air.   The issue here appears to be an unplanned for pressure difference.  I'm sure that by now you have concluded it is all in the air flow in these beasts and there are plenty of ways for that to get messed up.

The reason the clearance changes is that the stove won't be sucking its combustion air through the window and thereby possibly sucking exhaust into the house if an outside air intake is in use.


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## Dougsey (Jan 5, 2010)

Delta-T said:
			
		

> It is my belief that the cold intake air causes the gases that are being pulled toward the hopper (static negative pressure of hopper overcoming active negative pressure of combustion chamber) to condense and form the gummy material. I've seen gummy feeder on non-OAK setups, but far more prevailent on OAK setups.
> 
> And yes, add air tube and clean feeder, that'll do.



Delta-T, I don't understand how the hopper is pulling smoke into it. Isn't the pull in the direction towards the burnpot? 

When you open the hopper door, it seems like extra air gets pulled into the fire through the hopper.

Could you please further explain "static negative pressure of hopper"?


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## Delta-T (Jan 5, 2010)

Dougsey said:
			
		

> Delta-T said:
> 
> 
> 
> ...



I will try. During operation, yes, suction is toward the burnpot and as the vacuum pressure builds, air is pulled through the burnpot toward the fire. That same vacuum pressure builds in the hopper. When the vacuum pressure gets high enough is when the air actually gets pulled through the air intake and through the machine. The hopper is sealed, so that part of the machine stays at a relatively fixed negative, and all the air is pulled from the intake. This means that the vacuum pressure in the machine is greatest (generally) in the hopper (if we put magnahelix on combustion chamber, and in hopper we can observe this phenomenon) because there is no air (normally) being pulled from the hopper into the burnpot, via the auger tube. Changes in the negative pressure of the combustion chamber allow the greater negative of the hopper to pull gases toward the hopper area. Remember that in most types of air movement environments it is the path of least resistance that wins out. In this case, it is the path of most suction that wins. That help? This is my theory anywho.


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## Dougsey (Jan 5, 2010)

Do you think it works the same with inside or outside air but the problem is the outside air is cold and creates condensation?


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## Delta-T (Jan 5, 2010)

Dougsey said:
			
		

> Do you think it works the same with inside or outside air but the problem is the outside air is cold and creates condensation?



Yeah, I think it'll happen with or without the outside air, but cold outside air is like the icing on the cake, or gasoline on a fire (sneaky fire pun there).


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## vferdman (Jan 6, 2010)

Well, I have cleaned the stove's feeder and auger tube with hot water. It is now drying. Lots of gunk came out indeed. After I removed the burn pot in order to do this job, I realized that there is a gasket between the burn pot and the feeder. The original gasket is deteriorated and can not be reused. I called my local dealer and he is out of these things and can get one within a week. Argh! I will call another dealer tomorrow. I just can't imagine a week without this stove! Does anyone know if it would be ok to run the stove without the gasket for a week? I can reassemble without it and then pull the pot again and add it when it arrives.

I also performed the bypass mod. I did not bother with the tube and went straight for the 1/4 inch hole in the auger tube. It accomplishes exactly the same thing creating a shunt between the intake and the auger tube. In fact, post-2007 feeders all have this hole from the manufacturing. We'll see. I hope it all worked. Will keep everyone posted on this thread and after it's all done will probably post a new thread with my story. Hopefully it will have a happy ending.


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## Dougsey (Jan 6, 2010)

Vlad- Any pics?


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## vferdman (Jan 6, 2010)

Dougsey said:
			
		

> Vlad- Any pics?



No pics yet. It is really hard to work in that space. I will try, though. Taking pictures of the feeder windows is nearly impossible and that's where all the crud was. Now the windows look clean to bare metal. The mod I did was fairly simple to do and I will take some pics of that. Jury is still out on if it will work. I have not re-assembled the stove yet. I need to find that burn pot gasket and my local dealer is out of stock. Hang in there. I will follow up. Just a bit flustered right now with trying to find the gasket and re-assemble. It's cold and my wife is complaining...


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## Dougsey (Jan 6, 2010)

It would be a drive but Home and Hearth in Hampton Falls, NH would probably have it.


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## vferdman (Jan 11, 2010)

Hello, all. As some of you know, I have completed the cleaning and modification of my sticky/gummy Harman Accentra-2 stove. I have not posted in a couple of days in order to be sure that the results are not statistically insignificant. As of right now the stove has been running for several days without a shut-down of any kind. I have it set to 63 degrees in room temperature mode and outside intake air connected. This setup has never worked for me before (I've only had this stove for about 2 months) and it always shut down on lower temperature settings, especially if the outside temps were in the low-30's like the past few days. Low demand caused shut downs. Also, outside air caused a lot of smoke in the hopper (most noticeable when the fuel level is below 1/3 of the hopper capacity). I have taken the slide plate and auger out and have determined that I have the dreaded "gummy stove" syndrome. So, I set out to remedy the situation. The problem is that all the combustion gases backing up to the hopper (and filling it with smoke) eventually cause the feeder to get filled with gummy crud composed of pellet fines coagulated with combustion gases. When this gets bad enough the pellets do not come down the feeder into the auger as they should. In my case it was not bad enough to effect high demand situations where the stove is feeding lots of pellets. In low demand when stove only wants to keep a small fire going and feed a few pellets at a time it became a problem. I got shut downs every time there was low demand for heat on the stove (i.e. if the outside temps rose or I turned the room temp setting down or both). After several days of continuous running set to 63 degrees with outside air and no sign of any smoke in the hopper at any level of pellets (I almost let it run out of pellets and still no smoke) I am ready to declare success.

I have started a new thread that outlines the process I went through with some pictures, explanations and hopefully some discussion to follow. I hope this will help others as it helped me. I thank everyone who piped in with suggestions and helpful info as well as some (electronically) printed materials. The support I got from folks here has gotten me through this very new to me experience with great success. In the past few days I have become a very happy Accentra owner, which is a stark contrast to what my experience has been up to then.

THANK YOU, ALL 

Here is the link to the thread describing my cleaning and modification:

https://www.hearth.com/econtent/index.php/forums/viewthread/50345


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## dannjennyn (Nov 10, 2010)

You need the updated feeder installed that includes air tube. I had the same problem as you. I had smoke in the fuel hopper and what it was is the chamber above the auger and under the slide plate has creosote build up in it. This will start a fuel hopper fire if not attended to! Clean out the auger, auger tube, slide plate and that chamber by spraying creosote cleaner in it then put the air tube update on your stove and you should be good to go. The air tube update forces air into the auger tube and keeps the fire burning hotter and farther forward in the burnpot.


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