Harman P68 burnpot deteriorating.. again

[gvmelbrty]

I have a Harman p68 and at the end of this season, I will be replacing the burnpot for the THIRD time due to metal deterioration. I assume this is not normal and I’m getting tired of buying and replacing them!

FYI: A similar burnpot issue was discussed in this thread (01/2022): https://www.hearth.com/talk/threads/harman-p68-firepot-help.190694/ - but the cause was not determined.

After less than two years of use, the first burnpot was replaced by my local Harman dealer under warranty in 2015. The dealer said the burnpot must be defective.:

Four years later, the next burnpot was replaced by me in 2019:

Now, three years later, the burnpot is deforming again and will need to be replaced. Notice the raised mound:

It may not look like it, but the burnpot gets a daily scraping and then a thorough scraping/cleaning appox. every four weeks.

As for causes.. About the only thing I can come up with is the OAK (outside air kit) is bringing moist air in from the outside and causing rust in the burnpot (though I do not see rust elsewhere inside the stove). While the stove is running, of course the burnpot is very hot and any moisture should be immediately evaporated.. but that’s the only thing I can think of.

Should I try periodically oiling the burnpot with something (not WD40, my wife is chemically sensitive)? Or perhaps disconnect the OAK completely?

Thanks for any help.

 

[mtnbiker727]

Just curious, are you burning hardwood, or softwood pellets?

 

[Tonyray]

I have a Harman p68 and at the end of this season, I will be replacing the burnpot for the THIRD time due to metal deterioration. I assume this is not normal and I’m getting tired of buying and replacing them!

FYI: A similar burnpot issue was discussed in this thread (01/2022): https://www.hearth.com/talk/threads/harman-p68-firepot-help.190694/ - but the cause was not determined.

After less than two years of use, the first burnpot was replaced by my local Harman dealer under warranty in 2015. The dealer said the burnpot must be defective.:

View attachment 306743

Four years later, the next burnpot was replaced by me in 2019:

View attachment 306744

Now, three years later, the burnpot is deforming again and will need to be replaced. Notice the raised mound:

View attachment 306745

View attachment 306746

It may not look like it, but the burnpot gets a daily scraping and then a thorough scraping/cleaning appox. every four weeks.

As for causes.. About the only thing I can come up with is the OAK (outside air kit) is bringing moist air in from the outside and causing rust in the burnpot (though I do not see rust elsewhere inside the stove). While the stove is running, of course the burnpot is very hot and any moisture should be immediately evaporated.. but that’s the only thing I can think of.

Should I try periodically oiling the burnpot with something (not WD40, my wife is chemically sensitive)? Or perhaps disconnect the OAK completely?

Thanks for any help.

Ok. Have the P61A. 8yrs now of 24/7 burning in most of winter. Have been burning softwoods for 7 yrs of that time so rule softies out..even the box store low btu high ash stuff shouldn't cause rust.. have had an OAK since day one. Would rule that out.. the one thing I do is spray the inner walls AND BurnPot each spring after full cleaning with either WD or Pam cooking spray. Also I put 2 containers of damp rid in. 1 on the burnpot/ 1 in the big ash pan. I do get around 4 inches total of water in them come fall. Hope this helps as I have no rust anywhere I can see. Burnpot gets scraped once week either with flame or off. "You might concider scraping the burnpot more often. Can't hurt. Oh. Forgot this. I close off my outside exhaust with plastic food baggie and zip ties plus I cover my OAK opening outside also and Yet I still somehow accumulates 4" of water... my stove sits between 2 windows which are open in summer during no AC mild days. Must be some humidity getting in I assume...

 

[mtnbiker727]

How do you plug the pipe during the offseason?

I use damprid in my stove like @Tonyray suggested, and I plug my pipe with a Fernco cap, which provides an airtight seal.

 

[Mt Bob]

There always are a few installs, of different makes and models, that do this.
What bit I know- burning corn will do that.
Leaving carbon in pot over summer will do that, The carbon draws and holds moisture right to the metal, then it layers/flakes off when reheated.
Really bad pellets.
High temps will do that.
BIL has an old first series ST Croix Prescott, could not make it a winter without replacing or rewelding the pot. Why? when his was on, it was always burning on high, in his uninsulated leaky house/cabin. Also, it was the old, never upgraded analog controls.I gave them a P68, now they have variable heat, and it heats the whole place.
So, as yours has been doing this since new, and you are sure none of the other conditions apply, I would seriously consider replacing the exhaust probe and the control board.

 

[doneill127]

I think it looks like the metal has been overheated which has caused the distortion and high temperature oxidation (corrosion). Could be caused by insufficient airflow to keep the metal cool, wrong burnpot material, or burning something that’s burning hotter than the metal is rated for. Just an opinion.

 

[Cincinnati Kid]

Ok. Have the P61A. 8yrs now of 24/7 burning in most of winter. Have been burning softwoods for 7 yrs of that time so rule softies out..even the box store low btu high ash stuff shouldn't cause rust.. have had an OAK since day one. Would rule that out.. the one thing I do is spray the inner walls AND BurnPot each spring after full cleaning with either WD or Pam cooking spray. Also I put 2 containers of damp rid in. 1 on the burnpot/ 1 in the big ash pan. I do get around 4 inches total of water in them come fall. Hope this helps as I have no rust anywhere I can see. Burnpot gets scraped once week either with flame or off. "You might concider scraping the burnpot more often. Can't hurt. Oh. Forgot this. I close off my outside exhaust with plastic food baggie and zip ties plus I cover my OAK opening outside also and Yet I still somehow accumulates 4" of water... my stove sits between 2 windows which are open in summer during no AC mild days. Must be some humidity getting in I assume...

View attachment 306785 View attachment 306786

 

[Cincinnati Kid]

Ok. Have the P61A. 8yrs now of 24/7 burning in most of winter. Have been burning softwoods for 7 yrs of that time so rule softies out..even the box store low btu high ash stuff shouldn't cause rust.. have had an OAK since day one. Would rule that out.. the one thing I do is spray the inner walls AND BurnPot each spring after full cleaning with either WD or Pam cooking spray. Also I put 2 containers of damp rid in. 1 on the burnpot/ 1 in the big ash pan. I do get around 4 inches total of water in them come fall. Hope this helps as I have no rust anywhere I can see. Burnpot gets scraped once week either with flame or off. "You might concider scraping the burnpot more often. Can't hurt. Oh. Forgot this. I close off my outside exhaust with plastic food baggie and zip ties plus I cover my OAK opening outside also and Yet I still somehow accumulates 4" of water... my stove sits between 2 windows which are open in summer during no AC mild days. Must be some humidity getting in I assume...

View attachment 306785 View attachment 306786

Instead of purchasing Damp Rid every year, I purchased these metal desiccants. They last a very long time and you just heat them up in the oven and then put one in your stove. They absorb moisture very well.

Amazon product ASIN B0025OO8DO

 

[Tonyray]

Instead of purchasing Damp Rid every year, I purchased these metal desiccants. They last a very long time and you just heat them up in the oven and then put one in your stove. They absorb moisture very well.

Amazon product ASIN B0025OO8DO

Reading about sez needs activating every so often and best for small spaces.. maybe but I'll stick with 1 step method.

 

[gvmelbrty]

Thanks everyone for your input!

I've burned both hard and soft woods, but I'd say the majority are soft woods. My current pellets are softwood spruce. .. I have never burned corn or anything other than wood pellets. Could the pellets I use cause this burnpot issue? I'm not sure how to determine this, but I have used several pellet brands over the years and it happens regardless of brand.

About leaving carbon on the burnpot during off season - GUILTY! I always tell myself I'll do the big end-of-season cleaning in May-June .. but it always gets put off until Sept or Oct.. I had no idea that carbon left on the burnpot would attract moisture! ... Also, in Dec and January the stove gets left on 18hrs and sometimes 24hrs per day. So perhaps I need to scrape the burnpot more often.

During off-season I have not blocked the OAK intake - nor have I used any desiccants in the stove - and will try both this year - and a spray of cooking oil on the burnpot as well.

About a possible overheat situation... The vast majority of the time, the stove is burning with a small to medium flame and only runs with a tall flame for a couple hours during startup. ... ... Also, because of the location of the raised mound you see in the last picture above, I wondered if it was the igniter causing this? Although the original igniter was working, I replaced the igniter (w/ OEM) when I replaced the last burnpot in 2019. Is it possible the igniter is being keep on too long by the control board? (I watch the control brd LEDs and the igniter always turns off a couple minutes before the distribution blower comes on.) .. Or perhaps the metal deterioration happens on that particular spot because it was first weakened by rusting - and is therefore not caused by a faulty board or faulty exhaust probe (which I clean every four weeks)? .. But, I'm willing to replace both if necessary.

And concerning airflow.. here are some pics of the OAK and exhaust setup. I made the OAK-to-Harman adapter out of auto exhaust pipe. The local Harman dealer specified 4" diameter outside exhaust pipe to compensate for our high altitude (7000 ft). .. Exhaust pipe is swept every 1-ton (twice per year). ... I know there is some sort of airflow adjustment on these stoves, but I've never explored that.

PS: I have contacted the lead tech at my local dealer and I'm waiting for a reply (I'm sure it's a busy time of year for them).

 

[3650]

When I saw the pics of the pot I immediately thought it looked like an igniter issue. I wonder if the dip switches on the circuit board are set correctly.

Btw. Do you have a part number for that exhaust pipe you used. That’s exactly when I’ve been looking for.

 

[gvmelbrty]

When I saw the pics of the pot I immediately thought it looked like an igniter issue. I wonder if the dip switches on the circuit board are set correctly.

Btw. Do you have a part number for that exhaust pipe you used. That’s exactly when I’ve been looking for.

Pic of the DIP switches: 1. Up 2. Down 3. Up 4. Down

Outdoor exhaust pipe: DuraVent 4PVP-60 ; Length: 5 ft ; Diameter: 4-in.. (Note: This is 4-in diameter pipe, which was specified for our high altitude. You may get by with 3-in at your location. Contact your dealer.) ... Here's everything for this install.. (WOW.. some current prices have doubled or worse!).

 

[Tonyray]

Thanks everyone for your input!

I've burned both hard and soft woods, but I'd say the majority are soft woods. My current pellets are softwood spruce. .. I have never burned corn or anything other than wood pellets. Could the pellets I use cause this burnpot issue? I'm not sure how to determine this, but I have used several pellet brands over the years and it happens regardless of brand.

About leaving carbon on the burnpot during off season - GUILTY! I always tell myself I'll do the big end-of-season cleaning in May-June .. but it always gets put off until Sept or Oct.. I had no idea that carbon left on the burnpot would attract moisture! ... Also, in Dec and January the stove gets left on 18hrs and sometimes 24hrs per day. So perhaps I need to scrape the burnpot more often.

During off-season I have not blocked the OAK intake - nor have I used any desiccants in the stove - and will try both this year - and a spray of cooking oil on the burnpot as well.

About a possible overheat situation... The vast majority of the time, the stove is burning with a small to medium flame and only runs with a tall flame for a couple hours during startup. ... ... Also, because of the location of the raised mound you see in the last picture above, I wondered if it was the igniter causing this? Although the original igniter was working, I replaced the igniter (w/ OEM) when I replaced the last burnpot in 2019. Is it possible the igniter is being keep on too long by the control board? (I watch the control brd LEDs and the igniter always turns off a couple minutes before the distribution blower comes on.) .. Or perhaps the metal deterioration happens on that particular spot because it was first weakened by rusting - and is therefore not caused by a faulty board or faulty exhaust probe (which I clean every four weeks)? .. But, I'm willing to replace both if necessary.

And concerning airflow.. here are some pics of the OAK and exhaust setup. I made the OAK-to-Harman adapter out of auto exhaust pipe. The local Harman dealer specified 4" diameter outside exhaust pipe to compensate for our high altitude (7000 ft). .. Exhaust pipe is swept every 1-ton (twice per year). ... I know there is some sort of airflow adjustment on these stoves, but I've never explored that.

PS: I have contacted the lead tech at my local dealer and I'm waiting for a reply (I'm sure it's a busy time of year for them).

View attachment 306874

View attachment 306875

View attachment 306876

View attachment 306880

Burning softies would not be an issue as I posted before. They are quite a few ticks above most hardwoods. A year ago a part on my ignitor crapped out causing my ignitor to stay on . It never shut off till it finally blew out. Prob had been on a week or more judging by my big jump on electric bill that month so it took all that constant heat and did Not bubble or swell my burnpot. I am leaning towards leaving carbon bumps in the burnpot for so long but, can't prove it. Am sure u will attend to that more often now as it may Be the culprit..??

 

[Washed-Up]

One possibility after I’ve seen the pics of your oak, you are going from a smaller diameter to a larger diameter pipe, the pressure will actually increase as the flow slows down, potentially causing a hotter burn on the burnpot.

 

[gvmelbrty]

One possibility after I’ve seen the pics of your oak, you are going from a smaller diameter to a larger diameter pipe, the pressure will actually increase as the flow slows down, potentially causing a hotter burn on the burnpot.

Yes, I too wondered what were the repercussions of having of smaller diameter inlet hose for the OAK. The P68 manual states to use a 2 3/8-inch ID flex hose. The one I have is approx 2 inches (and hence the need for the adapter I made). I worried it was not providing enough air.

I'm just now reading about these air intake thimbles online and they all seem to have 2" hoses like mine.. BUT, the description for the thimble says the hose will expand up to 4 inches.. So.. If I removed my adapter and attached the hose directly to the stove, I wonder if that would make a difference?? .. I had no idea that hose would expand.. hahaha.. and all the work I put into that adapter 🤓. But, adapter or no adapter, the hose is still going from to 2-inches to 2-3/8.. so not sure if removing the adapter will make a diff, but I'm going to try it.

PS: Here's a pic of all the DIP switches.. 10101111. Board rev: 03-20-05886E, with a red wire ESP.

 

[gvmelbrty]

Burning softies would not be an issue as I posted before. They are quite a few ticks above most hardwoods. A year ago a part on my ignitor crapped out causing my ignitor to stay on . It never shut off till it finally blew out. Prob had been on a week or more judging by my big jump on electric bill that month so it took all that constant heat and did Not bubble or swell my burnpot. I am leaning towards leaving carbon bumps in the burnpot for so long but, can't prove it. Am sure u will attend to that more often now as it may Be the culprit..??

View attachment 306894

Interesting.. so a constant-on igniter didn't deform the burnpot metal? So that probably rules out the igniter as the cause.. Yes, I agree.. my leaving carbon and ash in the stove all summer is a large contributing factor, which I will remedy hence forth.

 

[Washed-Up]

Regarding your oak, you can enlarge the home fairly easy with a dremel, that’s what I’ve done with mine, I also run a 3” cold air intake hose and clamp it on my air intake stub on my P61A

 

[Tonyray]

Interesting.. so a constant-on igniter didn't deform the burnpot metal? So that probably rules out the igniter as the cause.. Yes, I agree.. my leaving carbon and ash in the stove all summer is a large contributing factor, which I will remedy hence forth.

Meant to say a part on my" circuit board" went bad causing ignitor mishap..

 

[shtrdave]

Not sure why I thought he burn pots were SS. But the rust ob the pictures tells me they are not or are like 430 or something.
I have had my stove for going on 11 years many times I leave my stove most of the summer without cleaning. I don't block the air intake. I see no type of deterioration on the pot. I just did a basic clean today and I always look at my pot, usually a mirror and and a light in the igniter area to see if the holes are open.

 

[rickwai]

I highly doubt it is from leaving carbon in the pot. I clean 2 -3 Harmans a day in the fall and 90% of them lay there all summer a mess and never see a burn pot like this. The only ones I use to see with burned up burn pots was the Pf100 furnaces. May have to do with the altitude? I know when the air is thinner it affects combustions, I just dont know which ways. I have always lived at normal elevations.

 

[doneill127]

Believe all steels oxidize matter of what temperature.
Based on the elevation and necking down of the oak consider getting a magnehlic and check the hi/low draft readings and adjust if needed. There’s a pot on the board to do this. Think the procedures in the manual.

GRADE	INTERMITTENT (°C)	CONTINUOUS (°C)
304	870	925
309	980	1095
310	1035	1150
316	870	925
321	870	925
410	815	705
416	760	675
420	735	620
430	870	815
2111HTR	1150	1150

Table Credit: ASM Metals Handbook

 

[Smiley67]

Are you buying the burn pots from your dealer? If so they could have a dozen or more and if they were part of a defective run they all would be bad. Try a burn pot from another source. Here is a stainless burn pot

• 
• 
• 
• 
• 

Replacement Harman Furnace & Boiler Firepot Newest Style Burnpot for PF100/PF120 and PB105-1-10-73403/1-10-73546A / 1-00-73560 Free Shipping​

Brand: HHT
4.7 out of 5 stars 9 ratings

---

$499.00$499.00

 

[Mr._Graybeard]

That pot is for the PF100 and PB105 boiler, which also had burnpot failures (bubbles/cracking). I had two replaced under warranty before Harman built one that stood up to the heat. I think the steel they use, 309 stainless, is the key to its success.

 

[gvmelbrty]

Regarding your oak, you can enlarge the home fairly easy with a dremel, that’s what I’ve done with mine, I also run a 3” cold air intake hose and clamp it on my air intake stub on my P61A

If it starts to look like my 2-inch OAK hose is the problem, that's what I'll have to do to get it up to the larger size.

Not sure why I thought he burn pots were SS. But the rust ob the pictures tells me they are not or are like 430 or something.
I have had my stove for going on 11 years many times I leave my stove most of the summer without cleaning. I don't block the air intake. I see no type of deterioration on the pot. I just did a basic clean today and I always look at my pot, usually a mirror and and a light in the igniter area to see if the holes are open.

I highly doubt it is from leaving carbon in the pot. I clean 2 -3 Harmans a day in the fall and 90% of them lay there all summer a mess and never see a burn pot like this. The only ones I use to see with burned up burn pots was the Pf100 furnaces. May have to do with the altitude? I know when the air is thinner it affects combustions, I just dont know which ways. I have always lived at normal elevations.

Interesting.. I would imagine that many "put-it-off-'till-Fall" pellet stove owners (like me) also leave their stoves uncleaned throughout the summer and there doesn't appear to be a rash of these deteriorating burnpot stories because of it. .. And, being that my location in NM has summer humidity amounts from 3% to 20%, it would seem less likely that this is the cause of my burnpot attack. .. And in fact, I just spoke to the tech at my local Harman dealer and he said he has only seen burnpot deterioration with the PF100(?) boiler stoves, regardless of proper end-of-season maintenance. .. That said, I plan to clean everything at the end of the season.

Believe all steels oxidize matter of what temperature.
Based on the elevation and necking down of the oak consider getting a magnehlic and check the hi/low draft readings and adjust if needed. There’s a pot on the board to do this. Think the procedures in the manual.

GRADE	INTERMITTENT (°C)	CONTINUOUS (°C)
304	870	925
309	980	1095
310	1035	1150
316	870	925
321	870	925
410	815	705
416	760	675
420	735	620
430	870	815
2111HTR	1150	1150

Table Credit: ASM Metals Handbook

Thanks.. I just read that section in the manual, "Low Draft Voltage Adjustment." To my knowledge, this test has never done. I'll ask the Harman tech if he'd be willing to do it.. or I'll try to get an air flow meter and do it myself. .. Does anyone know which meter I should get?

 

[doneill127]

Next trip out to the barn and I’ll take a picture. Need some1/8 tubing and I bought those fittings .