Help with my heater... burrrrrrr....?

You are correct, it is probably the "Flame Sensor" since the heater does ignite and fails after ignition.

The flame sensor is located on the OPPOSITE side of the bank of burners from where the IGNITOR is located. This is true on every heater or furnace. IE, it senses the ignition and flame up of the LAST bank of burners furthest away from the Ignitor.

You can clean that Flame Sensor with fine emery paper once or twice, but it will soon fail totally. Order a new one on www.heatcoolparts.com. If you dont know the part # get the model # , those are on a template on the SIDE of the unit inside and just far LEFT in the burner section. They have an 800 # for help.

On the backside of one of the access "covers" to the unit is a schematic of the gas/electronics system. Look for that. It is almost always on the back side of the air handler unless someone has torn it off, it is there.

You will not find a circuit on line. Try this source for help if you cannot resolve it yourself. http:/ths.gardenweb.com/forums/hvac On that site are a lot of retired HVAC people who can help you.

Try the website for the manufacturer. You may be able to download a manual or order one which would be far less costly than having someone do the repair for you. Heck, none of us want you to freeze.