Gas and Oil Home Heating Furnaces - Gas Furnace Lights runs a bit goes out

Ok I have a FAG furnace and I can't seem to keep the burner lit. It lights and runs for about 5 seconds and goes out again. The LED on the circuit board is flashing the call for heat. The house is cold, not unbearable but I can't get it over 67F. The thing is driving me insane, I can't see a reason why it would do this. The furnace is about 7 yrs old. Any ideas of what I should look for?
Thanks in advance for all replies.
Art
aka Caledon Jeep

Your type of furnace doesn't seem politically correct. What brand ? Does it have an inducer motor that keeps going when burner shuts off? (small motor on vent system)

It is a Lennox and there is a small motor noise right before it lights and then they both stop. It is very irritating to me, I am a mechanical designer by trade, heck I can make a robot place parts within a thousandth of an inch or weld to parts together but I can't figure this stuff out worth a darn.
There is a motor on the vent too. It never seems to come on, is that possibly the problem?

What is the step by step is this furnace doing?

Inducer fan starts (tied to the venting to ouside))
Spark/Hot Surface ignitor lights up?
main burners fires off??

typical way the furnace works
t'stat calls for heat
inducer motor starts and air proving switch closes.
pilot burns or ignitor lights up
main gas valve opens and main burner lites
flame proving sensor sends signal to control to keep main gas valve on
blower starts and the t'stat reaches desired temp
shuts down gas valve blower runs 1-3 min. to cool off heat exchgr.
blower shuts down

sounds like a flame sensing failure to me. Clean the sensing rod / ignitor with scotchbrite. look for loose screws and/or rust on the burner assembly that would interrupt the burner assembly's path to ground.
Has anyone worked on it recently? Maybe changed out the transformer?

ok, i wrote the other day, but didnt have much info. im not at the house where my furnace is, but i was looking at it today. so here goes...i will try to be detailed.
it is a York Stellar FAG furnace about 11 years old. it has the hot plate instead of a pilot light. last winter we found that we could maitain a pretty constant temp during the day, but at night the furnace would go off and sometimes not come back on. it would be freezing in the morning. (i live in denver area). anyway, this winter the same thing was happening. i thought it may be the electronic thermostat control (digital) so i replaced it. maybe i didnt get the wires on right. anyway, i noticed that the small control on the furnace with a dial on it that moves with the fan runs is acting strange. is this a fan timer? the other day it was coming on and moving and the furnace would kick on and run for a little bit. then it would shut off. the "timer dial?" would slowly move back to its original position, stop then start back again, kicking the furnace on. it was working ok, but the cycle seemed to be short on the "dial." i placed the thermostat on "On" instead of on "auto" and the dial stopped moving and the furnace stayed on. it was on when i left the house and was warming up inside. when i went back today it was cold again, and this time no matter what i did, the "timer dial" wouldnt move at all and the furnace wouldnt come on. im stumped. i dont know if i should replace this piece, rewire the thermostat (it is a 4 wire, by the way) or if it is just a setting on the "timer dial." i dont even know the proper name for this "dial" thing. anyway....HELP! brian

That dial thingy could be your fan delay / limit switch. If you're having problems with it then a service call is needed to inspect the unit for safety and to fix this problem. It could be a number of things causing your problem from a faulty fan delay to a failing blower motor, not to mention the problems that may exist with the air distribution. Your best bet is to get a service van in your driveway.

thanks for your advice

If the burners ignite and then promptly shut off, that is a problem with the flame sensing circuit if the furnace was previously working.

thanks. sometimes they run awhile. today they wouldnt come on at all. im pretty sure it is in the fan timer/control.