Unburned Coal in Ashes

Stoker Coal Boilers automatically feed the coal and have controls and pumps just like any conventions boiler. They are intended to be used as a primary heat and often have domestic hot water coils as an added bonus. They can be set up independently or in dual sytem with your existing oil/gas boiler. They can accommodate both hot water base board or steam plumbing.
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Posts: 18
Joined: Wed. Oct. 10, 2012 10:38 pm
Stove/Furnace Make: EFM

Post Mon. Jan. 13, 2014 8:39 pm

Hello All,

I have an EFM boiler that came with our house I purchased about 2 years ago......At the time my plan was to replace it, I'm sure glad I did not.
My question is that recently I've been noticing unburned coal in the ash tub......How can I correct this?



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Posts: 7385
Joined: Sun. Nov. 20, 2005 8:02 pm
Stoker Coal Boiler: Axeman Anderson 260
Hand Fed Coal Boiler: Self-built 'Big Bertha' SS Boiler
Baseburners & Antiques: Keystone 11, Art Garland
Location: Michigan

Post Mon. Jan. 13, 2014 11:14 pm

Hello Jim, welcome.
When you look at the burning fire in your EFM, is the fire round, symetrical, and is there a ring of ash around the outer ring of the firepot?

If the fire is oddly shaped, with unburnt spots then you probably have clogged air holes in the plates in the firepot. They sometimes get clogged with either rust or coal fines. Do you use the fines-lever every time you change the ashpan?

If you have the fire burning all the way to the edge of the firepot, with hot coals falling off the edge, then some may not be fully burnt..

BUT usually the black pieces in the ash that look like unburnt coal are actually shale in the coal.. they won't burn. To prove this, pick a handfull or two of the black, 'unburnt' pieces out of the ash pan, and put them back on the fire, on one side where you can see them be pushed to the edge of the fire by the fresh coal coming up from below. If it's shale, it will glow red, but when it gets to the edge, ready to fall off into the ashpan, it will be black, and look much like it did when you pulled it from the ashpan.

Did you change coal suppliers ? Some coal sources have more shale and ash, others less.

If the fire is misshapen, you will need to let the fire go out, and empty the fire pot, clean the holes in the tuyers, and if they are loose, warped or missing their pieces of rope gasketing, then they need to be resealed.. you want the combustion air to only have one pathway; the holes into the coal fire.

Greg L
Burning Pea/Buckwheat through an antique stoker [semi retired SSboiler],
Running an Axeman-Anderson 260M boiler burning Pea, About 150-250#per day
Farming, Fixing, Fabricating and Flying: 'spare time' what's that?

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Rob R.
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Posts: 11368
Joined: Fri. Dec. 28, 2007 4:26 pm
Stoker Coal Boiler: EFM DF520
Hand Fed Coal Stove: Hitzer 50-93
Coal Size/Type: Lehigh Rice
Other Heating: Dad's 1953 EFM Highboy
Location: Chazy, NY

Post Tue. Jan. 14, 2014 5:05 am

I don't have much to add beyond what Greg posted.

Just for kicks, would you mind posting your stoker, aquastat, and timer settings?

New Member
Posts: 18
Joined: Wed. Oct. 10, 2012 10:38 pm
Stove/Furnace Make: EFM

Post Tue. Jan. 14, 2014 8:08 pm

Hello Greg and Rob,

Let me first thank you for taking the time to reply is such detail.

Now to answer your questions Greg.

The fire is burning in a nice symetrical pattern and not oddly shaped and I do use the fines-lever every day.
The fire is not burning to the far edges of the pot, I have ash around the pot.
I did separate the black pcs. from the ashes and they did burn up......I'm thinking about 1/8 of the tub has the unburned pcs.
Still burning from the same pile I started with this season......Will need coal shortly.


The unit is a EFM 520....The Low limit is set at 175 and the high is set at 205 and to be honest with you, I'm not sure where to check the timer?

Again, thank you for the help,


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