Forced air furnace won't stay lit, blower blows cold air?

JimmyJam

Brian,

Remove the flame sensor and clean with steel wool for starters. It sounds as though you are not proving flame, and when the sensor accumulates enough white dust like stuff it will short cycle the burner.

Good Luck!
71Gibby

Brian_52

I recently moved into this house, and the furnace is about 5 years old, is a very small, and only needs to heat about 800 sf. The furnace has been kicking on, but the flame only lights for a matter of seconds. The blower continues to run the entire cycle (usually 5ish minutes), which means cold air is coming out of my vents. My ducts run through an unfinished attic, so yes, the air is COLD coming out! That's another issue, what I want to know is this: is there some type of internal thermostat in the furnace that keeps it from over-heating that may just need to be re-calibrated? I know the igniter is not the problem bc it fires up just fine; it burns for 4-6 seconds then shuts off. Please let me know your thoughts!

Timco

Your furnace does have a high limit switch...but your prob is the flame sensor. after failed ignition, or open roll-out loop or high limit, the blower will just run.

Tim

Brian_48

I awoke to a 50 degree house this morning, and as I jump out of bed, the furnace kicked on. This time the flame hit and stayed, and ran for nearly 45 minutes until the house temp came up to meet the thermostat. I stuck around until it cycled again, this time, problems all over again. Blower runs, 4 second flame. Does this still sound like the correct fix? I'll try cleaning it off this wknd.

Anna Conda

Yes, that does indeed sound like a flame sensor problem. If cleaning it doesn't do the trick, the next step is to replace the sensor. If replacing it doesn't do the trick, then the problem is likely in the control panel or a relay somewhere, and will require a pro.

daniel ( doctors heating & cooling)

i agree w/ all you guys, but one other thing i ran into is: if the ICM has been replaced recently there is a jumper wire that on some needs to be involved or not involved. just an expierience i had once?.

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