Lennox Gas Furnace - already replaced flame sensor and board

Old 03-05-13, 12:50 PM
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Lennox Gas Furnace - already replaced flame sensor and board

It goes through the normal start up sequence and when burner ignites it shuts off within a few seconds. Already replaced flame sensor. When that did not work, I replaced the board. Still does the same thing. AC works. Can anyone help me with what else could possibly be wrong?
Old 03-05-13, 07:31 PM
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Welcome to the forums !

With the flame sensor ....... the flame becomes part of the actual circuit. It's important that the sensor rod is actually in the flame.

The other important issue with the flame sensor circuit is the ground. The circuit starts at the control board > thru the sensor rod > thru the flame > to ground > and back to the control board. If the burner assembly or the control board is not grounded properly that could cause your problem.

Also...... does that control board have an LED diagnostic indicator ? If so .... any blinks ?
Old 03-05-13, 07:50 PM
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Does everything shut down before restart? May be the heat anticipator needs adjusting (if it has one)

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