Lennox 90UGFA3-75-5 Diagnostic help please!


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Old 02-22-14, 07:46 AM
J
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Lennox 90UGFA3-75-5 Diagnostic help please!

Hi

Last night my family and I smelled a burning smell similar to what you smell when you first fire up your furnace in the fall. I thought maybe it was the filters needing cleaning and resolved to do that today. Woke up this morning the furnace had stopped working sometime over night.
What I know so far:
Approximately 13 year old Lennox furnace- serviced regularily
I powercycled the furnace.
Got two slow blinking lights
Blowers kick on
I hear ignition
Stays lit for a brief time (under a minute)
Recieved two different codes (after cycling had second code)

First i got Low Flame Signal, Check Flame sensor.
15 minutes later, the furnace tried to light again on its own and i got
Primary/Secondary limit switch open

Now its sitting at watchguard burners failed to ignite.

Whats my next step?
 
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Old 02-22-14, 10:29 AM
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Clean or replace flame sensor.
 
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Old 02-22-14, 11:14 AM
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Welcome to the forums.

Serviced regularly ? The flame rod may need to be cleaned, which you can do yourself, but the burning smell and open limit suggest another problem.

If you power cycle and that code comes up again.... you may have tripped the flame roll out switch, which is push button resettable on many units.

Also check the filter as a high limit problem could be due to an airflow problem.
 
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Old 02-23-14, 09:01 AM
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Thanks for the replies. Turns out I had a bad relay that wasn't sending power to the main blower. This would overheat the highlimit switch and shut things down. Needs a new control board. For now the low speed blower is on 24/7 by jumping the wires until I can get a new board. Thanks all!
 
 

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