I have a Lennox G8Q3-80-3 gas home furnace that is about 21 years old. Everything works fine except the cycling of the blower. Furnace gas turns on when thermostat calls for heat, pilot lights the fuel with a nice blue flame, 2 1/2 minutes later the blower starts then stops after 30 seconds. Fuel continues to burn for 60 seconds, blower starts again, stops after 40 seconds. Fuel continues to burn for 60 seconds, blower turns on for 50 seconds then shuts off. This continues until thermostat reaches desired temp and fuel stops burning. Is this normal? What should the cycle be? What part do I need to replace?

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You have a flame sensor that may just need cleaning take out and take fine sand paper or emery cloth and clean

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This just sounds like a couple of problems. First, your blower is designed to only turn on once the heat exchanger heats up, so the flame will be on for a minute or two before the blower starts. it sounds like your blower is cooling down the heat exchanger too fast and causing it to shut off so it can warm up again...check blower speed for heat, it should be the lowest speed (black wire). Blue=medium speed, red= high speed. second problem could be your flame sensor rod is calcified, you just need to locate this and clean it off with some fine sand paper.it is located in the flames near the burners. Also change your filters, for proper air flow through your heat exchanger.

SOURCE: lennox furnace 17 yeanrs old. flame comes on and

I have a Lennox G40UH furnace. The burners fail to ignite about every 5th time. The furnace will try to ignite the burners then shut down. Once in a while the temp will drop down to 62 then fire up. I have only gotten a Diagnostic code once "Watchguard - burners fail to ignite" once I shut the power down and it started.
The furnace is clean, 5 years old, the flue is not clogged.

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hi check out the temp rise and fall on the fan control see if he has left the blower in the summer swich postion where it runs all the time

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You could have a bad overtemp sensor which is activating at too low a tempreture. They should not be that expensive. I would just replace it to eliminate the control if it is bad. It is a small metallic disc attached to the heat excanger. Has two wires coming off it. Approximately 1 inch in diameter. Usually on the front of the heat exchanger. It should have the tempreture that it activates at stamed on it. The temp is probably in celceus. Prior to replaceing it you could determine the activation temp and if you have a thermometer, or better yet an infared thermometer, check it while running to see what temp it activates at. If it is bad it will activate at too low a tempreture and should be replaced. Let me know if you need anymore help.

hardrocko

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