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

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

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).

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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?

investor7952 said:

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

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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?

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.

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.

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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.

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?

rickwa said:

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

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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?

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.

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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.