Excessive Carbon Build-up on Gas Fired Warm Air Furnace


Old 02-18-00, 10:40 AM
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HELP!!We have an Amana Air Command 80, Model GUI-D Furnace. We use allergy filters with this furnace. The furnace does not have a pilot light but uses an electric ignitor. Last weekend the furnace did not re-light but the blower continued to work. Turned down thermostat, waited awhile, turned it back up and furnace worked. However, when checking filter we found it was totally covered, back and front with carbon, as was inside of furnace. We cleaned off everything, replaced filter and now it seems to be working fine. This has never happened before. What would cause this excessive build-up and is it dangerous? How can we keep this from happening again?

[This message has been edited by jholland (edited February 18, 2000).]

[This message has been edited by jholland (edited February 18, 2000).]
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Old 02-18-00, 10:57 AM
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ok.... first off do you have a CO detector? do you burn candles?.... soot should not be coming , and covering both sides of filter.....I have found that candles burn in the home have caused this type of problem
Old 02-18-00, 11:15 AM
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No we do not have a CO detector and yes we do burn candles once in awhile.
Old 02-18-00, 11:20 AM
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are you sure it was soot..... the furnace cutting off was due to a problem in the furnace.... electronic control. flame sensor or what have you.... can you see the flame in the furnace? does it have a nice blue color? gas doesnt soot up unless there is some other problem involved.....like lint, or some chemical in the home that reacts with the flame....
Old 02-18-00, 11:32 AM
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Yes the flame has and had a very nice blue color.
Old 02-20-00, 08:36 PM
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Based on the reply postings thus far, for the most part I agree with them.

Professionially I feel an important fact was still missing.

Therefore, here's my two cents worth.

A plugged filter, as you discribed, will cause a furnace to shut itself off automatically do to a lack of cool intake air flow. Thus avoiding overheating and damaging of the internal firebox.

This explains why the heater didn't turn right back on when you turned up the T-Stat and why the fan continued running only.

The fan was cooling down the firebox. Once the correct internal temp. was reached, the high limit switch closed and allowed the furnace to fire back up. <This high limit switch is a built in safety feature on all forced air heaters.>

What happened is called "Cycling on HIGH LIMIT". I believe that is exactly what happened to your heater because your filters where not cleaned or replaced often enough.

Check the filter/filters monthly. Clean or replace as needed. Usually three times a year. Four or more times a year if needed.

What you saw on the filter and in the blower compartment was not carbon caused by the furnace burners. However, it was dust, lint, etc. built up over a long time do to a lack of periodical maintenance.

You mentioned allergy free filters. These type of filters contain activated charcoal.
This is most likely what you saw and referred to as SOOT.

So go ahead and burner a candle. They will not cause that much soot to clog a fyrnace filter.

Hell, if those candles did burn with that much soot, you would see it also collecting on the furniture and walls.

Regarding a CO Tester. Save yourself the problems and that money.

TomBartco Enterprises.
Trade:Natural Gas Energy Consultant & Technician.
Appliance Service & Repairs Rep.
Vocations:Saw & Tool Sharpening. Small Engine Repairs.
Accurate Power Equipment Company.

Personal Quote:
"Drive Safely. The Life You Save, May Be Your Own."

[This message has been edited by TomBartco (edited February 20, 2000).]

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