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[jreimer]

It's not really that hard.  I can crush it in my hand then it turns to powder.  It is hard enough to plug the nozzle though.  This morning I took my cleanout shovel and scooped out the hard ring of ash from around the nozzle again.  It forms every load as a doughnut around the nozzle.  I'm using the same wood I used all of last year and never experienced this before.  Very strange indeed.

Thinking of the wood, I am burning a lot of medium sized unsplit sticks that have the bark on them, so perhaps I could be burning more bark than usual.  The wood is clean and not dirty.  Perhaps there is something strange in the elm bark that is causing this?  But why only around the nozzle?

[coolidge]

Are all the air holes clear in the firebox, I believe there are 13 of them. If so try giving the fire box air a little more, maybe out 6 turns.

[slimjim]

I'm curious, do you have the ability to try some different wood?

[jreimer]

Ok, so I did my weekly cleaning last night.  Nearly 8 gallons of ashes!!  I'm going to experiment with a lot higher airflow settings with the same wood and let you know how it goes. 

[coolidge]

How did you make out with your air flow settings?

[jreimer]

Sorry I haven't posted for awhile.  Been busy with family, Christmas, New Years and fighting the COLD!!!  Man it's been cold here and the wood has been flying through the furnace.   Highs of -15F and lows of -35F for weeks with some -40F's thrown in there for fun.

Anyway, the higher air flows haven't changed the crusty ash issue.  In about a week I will have run out of elm and will be using ash.  I'll see if that makes any difference. 

[slimjim]

You might want to turn the air back a bit if you start getting 1/2 inch or larger pieces of carbon on the shelf above the vertical tubes

[jreimer]

So it looks like the culprit is the elm that I have been burning.  I have switched over to the ash portion of the woodpile and this hard crusted ashes phenomenon appears to be nearly eliminated. 

Posts on some other forums seems to support this as well, as others have reported the same hard ash chunks when burning elm at high temperatures.  This would explain why it was only forming around the nozzle as that is the hottest section of the firebox.

A chemical mystery with elm I suppose...

[mlappin]

Depending on the species of elm I've had a few amishmen tell me that elm collects calcium out of the soil more so than other trees. A really good hard elm thats dry seems to dull a chain faster than other woods. Your chunks of hard ash could have some calcium mixed in the ash and fire baked so it would get hard.

[jreimer]

Well the elm problem hit me again last night.  I have been mixing in a few elm splits over the past few days that were mixed in with my spruce pile.  This morning I go out to fill the stove and it's at 108 degrees.  Half a load of wood left and smoking like crazy. 

The ashes had crusted around the nozzle enough to partially plug it up.  Very frustrating when it's -24 Fahrenheit at night!  This hasn't happened in 2 years since I stopped burning the elm.  Anyone else experience this with a certain species of wood?

[mlappin]

Interesting, I’ve been eyeing several dead elm, I’ll cut em up and burn nothing but elm for a few days and see what the G400 does with it.

[martyinmi]

I really don't think this problem is a wood species problem at all. I've burned a crap ton of dead Elm in my stove and I've not noticed my boiler behaving any differently than with any other species.
 My nozzle used to partially plug once or twice a year as described, but I've always attributed it to dirty wood(think "muck" from the woods).
I take the hoe that came with my boiler and poke it's opposite end through the nozzle and make sure it is thoroughly clean at least once a day now. Problem solved.
I know the folks at P&M don't want us poking anything through the nozzle, but I don't really care.
I use nozzles made by KarlK, and they last almost twice as long as the ones from P&M. They aren't nearly as susceptible to damage.