Lennox Gas furnace

THeavrin

My Lennox gas furnace tries to come on but burners won't stay lit?

Houston204

Clean the flame sensor.
It will have a single wire connected to it.
Avoid the ignitor, it is easy to break and will also be located in front of the burners.

how

Age and model would help.

Look on the furnace through a grill or inspection port for a flashing led light. That flashing light sequence will match a legend on the door that will point to what the furnace problem is. Tell us what you find.

Doc Holliday

this. happens on all (older) gas furnaces from time to time. that little rod is inolved with flame rectification, dc voltage to ground through the flame. let's the furnace know that there is a flame so the call for heat (gas valve) remains on. once sut and corrosion builds up on the flame sensor it interferes with the sensing of the electrical signal the board needs to keep the call for heat on. It's telling the control board there is no flame so to cut the gas off.

anyways, hvac flame senser 101 over and out. easy monkeys. clean it and you will have heat. GoOd lUck.

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Thanks.

Houston204

Modern furnaces still use flame rectification.
Since the flame sensor requires a good ground, it is also a good idea to remove power and wire brush the ground connection entering the furnace and the ground connection on the burner area.

I always get a lower microamp DC reading with Lennox furnaces than other brands. I get 5uAdc with Carrier using OEM boards and 2uAdc with Lennox.
.5uAdc is all that is required with the models I usually service.

I have seen ICM replacement boards for Carrier ask for more and get less.

Doc Holliday

I know. What I meant is with older furnaces that have older flames sensors the cleaniing is not an uncommon thing. I'm not going to need to clean a brand new flame sensor in a brand new furnace in other words.

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Thanks.