Furnace shut down

Old 10-23-03, 08:42 PM
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Question Furnace shut down

Dear Experts:
I have a one year old Concord (Lennox) 80% gas furnace that shuts down about 5 minutes after kicking on without reaching the shut down temperature. I can get the furnace to restart for another 3 minutes by turning the thermostat Heater switch to off then on again, which resets the furnace.
It did this at the beginning of last winter with the solution being the replacement of the dirty air filter. This year, I have the same problem but a new clean air filter did not solve it.
The sequence of operation:
Reset Furnace by turn thermostat heat switch off than on again.
After a 15-second pre-purge, the control energizes the hot surface igniter.
After warm-up period, the main gas valve energizes and the main burner ignites.
The air blower energizes following a 30-second delay.
After 5-minutes, the burners shut down.
45 seconds later the blower shuts down.
The last time I restarted the furnace, it went through the aforementioned cycle and then the blower clicked on again and 15 seconds later the H I S reignites
The built-in self diagnostic system is showing a failure code for an open limit switch or limit switch circuit.
Here are the specs of the furnace:
Concord (Lennox) 80% Gas-Fired Furnace
Model: CG80UA
100,000 Btu
Natural Gas
Instant Start

Any Ideas about what is wrong?

Old 10-24-03, 04:17 AM
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You probably have a clogged/partially clogged heat exchanger or flue/chimney, if you have a/c could be dirty coil. Also check the returns and make sure they are not covered and the supplies are all open.
Old 10-24-03, 03:55 PM
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i would check that coil, something is restricting the airflow, or the limit is weak. concorde is owned by lennox, but different product. low end.........sorry!

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