Harman XXV burning rich

[ddirocco]

Hi all,

I have been wrestling with an old Harman XXV (2004). It seems to be burning rich, leaving soot on the glass and heat exchanger. I have replaced the combustion blower motor and fan, new burn pot, new flame guide, new ESP sensor, new gaskets all around. It was installed with an OAK, which I recently disconnected because it seems to burn a bit cleaner with room air. No obstructions that I can see. Direct vented with only about 2 feet of pipe so easy to clean and see into.

I have tested the draft with a magnehelic and get good draft at the low and high draft setting in test mode. About 0.55 in low and 0.65 in high. During test mode the combustion blower light gets brighter when it is on high but no matter how hot I burn the stove it never goes off the dim (low) setting. Does anyone know if the light means anything during operation? Could the board be bad and not engaging the high draft?

Any thoughts would be much appreciated.
Thanks

 

[Washed-Up]

Light brightness doesn’t mean anything as far as I know. Have you tried different brands of pellets? And when you do a clean do you make sure the holes in the burn pot are as open as possible?

 

[ddirocco]

Yea I switched to super premium brands this year as I thought that might the issue. Some are certainly better than others but all eventually lead to the same result. I have Easy Blaze and Barefoot currently. I clean the burn pot holes every day before I start it up.
Thanks for the thoughts.

 

[Washed-Up]

Also, check the flapper on the air intake at the back of the stove to make sure it moves freely

 

[ddirocco]

Yup. Did that when I took off the OAK.

 

[Washed-Up]

It seems odd to me that it is better without the oak, cooler air is more dense and should help. Your combustion fan sounds like it’s spinning as fast as it always has?

 

[ddirocco]

We moved into our current house a year ago and when I first went over the stove I noticed the OAK was clogged with a piece of insulation. I ripped it all out but I wonder if here isn’t something in there I am not seeing. That’s my best guess because I agree with you that it should be better with cold outside air. It’s hard to say if the combustion blower has been always running this same speed but according to the manometer, I have more than enough draft.

 

[rickwai]

I would have to guess it needs a board? Sounds like everything else is good. A .6 inwc or more in test is great

 

[ddirocco]

So I finally resorted to putting in a new board. The combustion light doesn’t change, same as the old board, so that must just be how it functions. This new board does seems to have slightly different logic in how it feeds pellets, especially at start up. I’m thinking pellet quality might just be inconsistent as everything else checks out fine.
Thanks for all the suggestions!

 

[ddirocco]

Wanted to provide a quick update to close this out. I believe the root of the soot problems stemmed from me overlooking the feed rate. With the softwood pellets, which are shorter and have more btus, I needed to turn feed rate down to 2.5 to achieve clean burn. It seems these small pellets tend to pile up in the burn pot which reduces combustion air. Even though they aren’t getting pushed off, the lack of air makes the stove call for more pellets which ultimately leads to more soot. Hope that’s helpful to someone with the same issue.

 

[Harman Lover 007]

Wanted to provide a quick update to close this out. I believe the root of the soot problems stemmed from me overlooking the feed rate. With the softwood pellets, which are shorter and have more btus, I needed to turn feed rate down to 2.5 to achieve clean burn. It seems these small pellets tend to pile up in the burn pot which reduces combustion air. Even though they aren’t getting pushed off, the lack of air makes the stove call for more pellets which ultimately leads to more soot. Hope that’s helpful to someone with the same issue.

Doesn’t sound quite right to me but OK. Just for kicks, is the cover on the burn pot installed correctly? It installs from the top under the wing bolts not the bottom. (Been there, done that)
And for the record, the Harman Feed Rate is the most misunderstood adjustment on a Harman stove. You shouldn’t have to adjust it that much to get your stove to operate properly. Just in case you haven’t read it, click on the link in my signature and scroll to the description of feed rate. It’s very helpful.

 

[ddirocco]

I do have the cover installed correctly. Also, I have read your post on the Harman operation, it is helpful indeed. I bumped the feed rate to 3 today and it still seems fine. At 4 is when I noticed things going south. I am also going to take a closer look at the fines cover tonight as I noticed plenty of threads pointing to that being a leaky spot.

thanks again

 

[rickwai]

I do have the cover installed correctly. Also, I have read your post on the Harman operation, it is helpful indeed. I bumped the feed rate to 3 today and it still seems fine. At 4 is when I noticed things going south. I am also going to take a closer look at the fines cover tonight as I noticed plenty of threads pointing to that being a leaky spot.

thanks again

That is what the feed rate is there for. To adjust for different pellets. The short hardwood Sommersets have to be set lower because they feed better and burn hot compared to a longer pellet

 

[Harman Lover 007]

That is what the feed rate is there for. To adjust for different pellets. The short hardwood Sommersets have to be set lower because they feed better and burn hot compared to a longer pellet

To each his own....the overwhelming majority of Harman users should be somewhere between 3 and 4 on the feed rate. No matter what they are burning. Otherwise you will not be able to get the optimum performance that your stove can provide. Just like putting a brick under the accelerator pedal of your car....

 

[ddirocco]

I am completely open to other suggestions. If you don’t think feed rate should have that much to do with it, what have I missed? Draft/vacuum is perfect. No obstructions in venting. New combustion blower, burn pot, flame guide. All new gaskets. Burning high quality pellets. Maybe I am just asking too much from the stove? I just didn’t think soot all over the heat exchangers was normal.

 

[rickwai]

I am completely open to other suggestions. If you don’t think feed rate should have that much to do with it, what have I missed? Draft/vacuum is perfect. No obstructions in venting. New combustion blower, burn pot, flame guide. All new gaskets. Burning high quality pellets. Maybe I am just asking too much from the stove? I just didn’t think soot all over the heat exchangers was normal.

Exactly. Cut your feed back a little to find the sweet spot.