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Old 02-08-2007, 04:25 PM   #1
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Furnace - fan comes on, but no heat


I know...don't blame the thermostat. Bought the house out of foreclosure...prior homeowner replaced the thermostat and don't think the heat has worked since. Today, the fan powers on when placed on auto but the burners never fire. The evacuation fan in the furnace also does not power up. Thinking he crossed a couple of leads or failed to use a jumber when necessary? Please help.

Furnace is a Lennox 80UHG...will get info on the thermostat. Don't know the wire quantity just yet.

Thanks,

Allan

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Old 02-08-2007, 11:36 PM   #2
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Furnace - fan comes on, but no heat


Check for a tripped limit switch. If the furnace ever gets too hot, a limit swich trips, causing the furnace blower to run continuously to cool it off. Some are automatic reset, others must be reset by pressing a button, and some must be replaced. Look in the furnace manual, and it should say how to reset it. Also, look for a diagnostic code on the furnace control board. If there is no fault code, it might be a thermostat wiring problem. G is usually the wire that turns the fan on.

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Old 02-09-2007, 08:31 AM   #3
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Furnace - fan comes on, but no heat


Okay...good to see I am on the right track. You are also correct. Troubleshooting fault code indicates: "Primary or Secondary limit switch open". Now I just have to figure out how to reset...nothing in the manual says how to reset. Any good resources out there on Lennox and limit switches?

Thanks Again!!!

Allan
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Old 02-09-2007, 10:32 AM   #4
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Furnace - fan comes on, but no heat


Come to think of it, the filter was VERY plugged when I bought the place. So I have now replaced it but clearly need to reset the limit switch. How do I reset a limit switch?

Thanks

Allan
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Old 02-09-2007, 09:08 PM   #5
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Furnace - fan comes on, but no heat


could be as simple as disconnect power to furnce then power back up.let us know.
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Old 02-12-2007, 03:37 PM   #6
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Furnace - fan comes on, but no heat


Look in the manual for the location of each limit switch. After the furnace is CLEAN, press the little button on each one. One of these will probably click when you find the tripped one. Automatic reset ones do not have a button.

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