York furnace would not maintain burner flame. When performing initial trouble shooting removed fan compartment panel disengaging safety switch. Cleaned flame sensor and furnace maintained flame for 4 days of cycling. Last night the fan compartment panel fell open... didn't get properly 'hooked' after trouble shooting; properly reinstalled panel.
Now furnace wants to simply re-start with full fan as if burner was on, no ignition cycling.
Suggestion?

Check for loose wires.

Check for loose wires.

No loose wires; went through both flame sensor coupling, limit switches, gas valve and wiggle all connections on control board. Also control board (White Rodgers 50A50-241) is NOT flashing any errors.
Frustrated.

When the compartment fell open did wires come off? If so did you put the wires back on correctly. I am just looking for the simplest fix for what should be a simple problem. The daggon furnace ran OK for 4 days before the cover event so it should run now. You might check all wiring continunity especially since they might have come under a strain when the cover popped open and fell down.

Thanks... isn't it fun to troubleshoot weird/intermittent things! The safety switch is a deadman's switch bolted to the cabinet frame. The panel, when in the frame, depresses the button and closes the circuit. That was one of the first things I thought of and checked out. Wiring show continuity on each side of switch and closed circuit when switch is depressed.
I'm beginning to think the flame sensor, even though cleaned, is acting more weirdly than usual. Think I'll re-steel wool it and see what happens.

Door falling off killed power to furnace. If this happened when furnace was in full fire, the heat from the heat exchanger probebly tripped an auxiliary limit switch(usually located on or near blower squirel cage). These limits usually have two wires going to them, and in between the two wires there is a small button that can be pushed in to reset the limit.

Any luck so far?

Nope. Tried resetting, nothing and a tap-tap-tap and nothing. I'm going to try steel wooling the flame sensor again just for old time's sake.

Just thought I would mention that this board is not the same as the board in your furnace but a replacement.

http://www.white-rodgers.com/wrdhom/pdfs/instruction_sheets/0037-6265.pdf

After a long afternoon and evening of trouble shooting and not being successful, was sort of frustrated and rather firmly 'popped' the control board by the 12 pin connector. Wowser... furnace went into ignition mode immediately. Investigated the 12 pin connector area some more and found that one of the male pins on the board was loose and that if things were just 'right' furnace would run. Couldn't get to the proper area of the connector to re-solder but sat on the floor and was able to tug on the connector to generate heat. New board yesterday morning, so far furnace hasn't missed a beat and temps have gone into the teens. Parts man said he had never see a White Rodgers board fail exactly the way this puppy did.

Happens to the best of them. Could get worse, too.