Gas and Oil Home Heating Furnaces - Burner turns on for 30 seconds then off

Furnace is a goodman ck-30-1 installed in May / 95. The problem is that you set the Honeywell thermostat at 68. the furnace cycles thru to start. The igniter starts and the burners go for about 30 seconds then shuts off. the blower keeps running for awhile, just blowing cold air. Any suggestions as to what it could be? This year is the first we have upped and downed the thermostat to save money on gas bills.

This year is the first we have upped and downed the thermostat to save money on gas bills.

That's not likely to be the problem.

Did you time the 30 seconds?

What color is the blinking LED on the control board?

The burners go for about 6 seconds then blow out. the tempurature keeps dropping, never making it up to 68,where the thermostat is set. so I turn the thermostat back to 50 then immediately back up to 68. and the process starts all over again. I have to babysit it. Where is the LED at?

The burners go for about 6 seconds then blow out.
That sounds like failure to detect flame during the trial period.

I turn the thermostat back to 50 then immediately back up to 68. and the process starts all over again. I have to babysit it. Where is the LED?
Does your furnace have a "computer board"? It could be behind a tin panel so that you can't touch it if it is not a sealed unit.
You might open a safety interlock switch as you remove panels to locate it.
You will have to replace the panel or hold the button with your finger to get your furnace to work at all.

I found an old toothbrush and cleaned the flame sensor and presto - heat
Thank you for your help I learned alot about furnaces.