PF100 and PB105 Burn Pot Issues

Check out this thread on the Corn Burners forum. My latest stainless steel burn pot will need replacing (under warranty) pretty soon.

http://www.iburncorn.com/new-forum/27-harman-stove-company/7396-pb-105-burnpot?limit=10&start=10

4 th winter here with pf100 the burn pot was fine in early nov. no bubbles or cracks, now there is a bubble and crack from hole to hole about 3 holes long, I have a possible idea as to what caused mine to bubble and crack, I let the furnace run completely run out of pellets while in auto-light as the furnace ran out of pellets it tried to light itself with no pellets in pot and did this for some time making the pot extremely hot, hot enough to bubble and crack I had checked the pot only 1 or 2 days prior to letting it run out of pellets and the pot was fine and now bubbled and cracked.

The burnpot bubble issue hasn't been resolved yet but..........My dealer has mentioned to me that for the past month Harman has been testing a PB-105, checking temps within the combustion area to see if they can determine what is causing this issue with the burnpots. The testing has shown that the pellets that were used, the temps ranged from 700*F to 1200*F depending on which pellets were being used. I suspect the temps could be higher yet using a good softwood pellet. The stainless steel that is now being used to manufacture these burnpots is rated at 1100* heat resistant, IMHO,(Harmans too) the reason that the burnpots are failing. My dealer told me that Harman will be using a different steel alloy trying to correct the issue, I should be receiving one of these very soon to test.

I just noticed when I cleaned mine a week ago it is starting to bubble ever so slightly. It's been installed a year and I've burned through about 4.5 tons of Lignetics green label.

When should I report it to my dealer so they can order a new burnpot, when the cracks start forming between the holes?

I'm not sure stainless steel is the right material for the burn pot, it has a higher linear expansion coefficient than regular steel.

I think Inconel or a similar type nickel-chromium alloy would do the trick and survive the temperatures our PB-105s dish out, the same material is used in turbocharger exhaust turbines and jet engine turbine blades.

Before I installed mine, I wrote Harman an email and said I had heard there was a problem with the burn pots in the PF100 and asked if they would consider sending me a stainless steel one. They told me that with normal maintenance, the regular burn pot was fine and I got nothing. To be honest, I'm not impressed so far with Harman's customer repore. The couple of times I've contacted them, they seem to be a little too high and mighty regarding customer issues and their answers are pretty short.

If the pellets reach charcoal stage they will get above 1100 °F.

How often should you scrape the burn pot? Seems if I don't do mine for a couple days, I get a lot of heavy carbon build up when I do scrape it. I'm using Okanagan pellets.

Ejectr said:

How often should you scrape the burn pot? Seems if I don't do mine for a couple days, I get a lot of heavy carbon build up when I do scrape it. I'm using Okanagan pellets.

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I get some carbon build-up on the bottom of the burn pot. The build up varies with different pellets.

What works best for me is what Red does. I took a long heavy duty screwdriver and ground the end to a sharp point. When I ram that down in there over and over again it does a good job of digging into the buildup and knocking it loose. It's tough stuff. The scraper just rides over the top of the buildup.

Thanks for that advice. I'll be doing the same.

If you scrape the burn pot wth a fire in it and extinguish the fire, how will it re-ignite?

wil said:

The burnpot bubble issue hasn't been resolved yet but..........My dealer has mentioned to me that for the past month Harman has been testing a PB-105, checking temps within the combustion area to see if they can determine what is causing this issue with the burnpots. The testing has shown that the pellets that were used, the temps ranged from 700*F to 1200*F depending on which pellets were being used. I suspect the temps could be higher yet using a good softwood pellet. The stainless steel that is now being used to manufacture these burnpots is rated at 1100* heat resistant, IMHO,(Harmans too) the reason that the burnpots are failing. My dealer told me that Harman will be using a different steel alloy trying to correct the issue, I should be receiving one of these very soon to test.

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These photos are of the new and improved (maybe)burnpot that was installed in my PB105 boiler today. It appears that the burning surface is still stainless with cross bracing welded to the bottom.

Thanks for the great pictures Wil. It would appear that with the added bracing to the bottom side it would no longer be possible to use use the original igniter with the fins. Would you agree Wil? I remember that you were given one of the new air pumps to see if that would resolve the issue. This could get interesting.

Looks like a different convection air hole layout. Where will the finned igniter go for those that don't have the hot air ignition. Hope this is just an experiment and not a band-aid fix! Thanks for the update Wil.

Also, is it possible that the reason why some folks did not have the burnpot issue untill after 4 year or so is because the pellets they use were not capable of the hotter temperatures thought to be responsible for the bubble?

Forgive me for butting in, just a guess those cross braces look like they are adding a heat sink into the colder combustion air to cool off the pot under the fire.

Centurion said:

Thanks for the great pictures Wil. It would appear that with the added bracing to the bottom side it would no longer be possible to use use the original igniter with the fins. Would you agree Wil? I remember that you were given one of the new air pumps to see if that would resolve the issue. This could get interesting.

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Yes, I do have the pressure ignition system installed in my boiler, I really like this, ignites quickly. I agree, the finned igniter couldn't be used with this burnpot.I have some mixed feelings about this being a band-aid fix, my thoughts were to have the burnpot burning surface with a higher heat resistant steel alloy. I know that this nickel alloy metal is very expensive but.....it's very possible that the thoughts were that these cross braces will act as heat sinks to lower the temps on the burnpot, maybe. I was told by my dealer that during testing that Harman discovered that different pellets burned at different temps (surprise, surprise) so.... my guess is, yes, depending on what pellets one is using determines the time prior to a bubble forming.

http://www.onlinemetals.com/merchant.cfm?id=880&step=2&top_cat=131

Greetings - newbie on the site, but I've been looking over threads for a few months now. I have a PF100, installed last December. I started it up about two months ago, before Halloween, and I am just now getting the start of a bubble. I clean the burn pot every other day. Right around the time I changed pellet brand recently, I noticed a lot of carbon was built up at the bottom of the pot. Once I got it scraped off, I found the bubble.

I've experienced some changes this year over the behavior last year and I am wondering if any of them are further related to this.

Last month I have had a problem with the distribution fan limit switch. I was able to get my dealer to provide me with the part. The new one is better but acts differently. I set it per the manual, but it was cycling the fan pretty often, like one minute on, one minute off. I decreased the lower limit setting about 10 degrees and it seems to be better now.

I cleaned the cumbustion blower before I replaced the limit switch in case I was not getting a good mixture. It was not too bad and I didn't note any change in the flame height after the cleaning. I cleaned out the chimney before start up and have it scheduled to do again this weekend. The chimney is 4 feet vertical and 8 feet horizontal. The basment Bilco door is not very well sealed (yet) so we don't need an outside air kit (yet).

Went through about 2 tons of pellets last year (January to April) and almost a ton so far this year. My house is relatively new construction, only 1400 sq.ft. and well insulated, with a good southern exposure for heat efficiency.

At the end of the season last year, when the unit had to cycle more often becasue of warm days and cold night, the ignitor burned out. It was the old style ignitor, and a new style igntor was installed.

I bought a ton of pellets from a local distributor and another from Lowes last year. I bought some from Walmart this year that claimed to be Premiun Hard Woods, but the ash content was much higher that what I had last season. I am trying a really low ash brand from a stove shop for my current fuel.

So I wonder if any of these three things could be a factor in the burn pot failure:
new ignitor
failed fan limit switch
cheap pellets
(Now the really fun part is going to be getting a service call scheduled. :-S )

Welcome to the forum Ar-ef-bee; good to have another PF100 owner participating here. Getting to be quite a few of us. Was curious if your distribution fan control/ HI limit switch is located 11 inches above the top of your furnace cabinet and mounted on center of the duct? If not you may have to compensate for it being out of position for the factory adjustments. You may need to have a certified HVAC person adjust it for the correct fan control and high limit set points. You could copy his settings and how he figured it. The High Limit adjustment is an important safety feature that will shut down the fuel feed to the furnace if the duct temperature gets too high.

Also this would probably get a better response if you started a new thread.

Thanks for the prompt reply! I really brought this up here because it seemed to be a pre-cursor to the bubble forming in the pot.
Actually the fan limit switch is placed exactly as the manual requires is and I didn't fool with the high limit. I realize how important that is.

Red Devil said:

Still hard to believe with all the problems with the burn pot bubble, that this being my 4th year for the PF100,
both mine and my sons, we have not had any issues with the bubble.
When the burn pot is cleaned, that is the first thing that I check.
I have used various brands to pellets.
Doing something right, praying to the right person....NO, you can't have their name...haha

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I know that you run your furnace in manual, continuous burn, hmmm, I'm wondering if this might be the reason why you aren't having the issue with the burnpot.

This may sound odd, but what chimney type and length are you using Red D? My thought is that back pressure from a long chimney could keep the heat from dissipating in the fire box, causing the steel to heat past it's recommended use.
If your prayers go to the church of the Steelers, that would explain a lot.