I have a Rheem Classic Series Super Quiet 80 gas furnace. My problem is the furnace will turn on burner fires for a couple of seconds then burner turns off and fan blows. This cycle cotinues and eventualy the left LED blinks and I reset the power. This heater has been nothing but problems for the last 4+ years. Is there a solution other than replacement?

Not sure but its possible your thermo coupler is shot and needs replacing. If you have a pilot light it could be out but the furnace should not start if the pilot is out as there should be no oower getting to the controls unless the pilot is trying to let it start. A bad thermocoupler will not let the flame start.

I presume you're talking about a gas furnace, even tho the title says Rheem gas water heater. Either way, it works the same for both.

Any black coloring on the heat exchanger is *not* from overheating. Black is from a sooty flame caused by a mis-adjusted burner. (In fact, a sooty flame is less hot). There is an adjustable "air intake plate" for air to enter the burner where the gas enters the burner. A proper flame is made by adjusting this air opening so the proper gas/air mixture feeds into the burner. If the air vent is closed too much it produces a sooty flame.
The age of the furnace is the most important aspect, and that helpful to determine a likely condition of the heat exchanger and burners. Other than a badly adjusted flame, the main thing to watch for is a badly rusted out heat exchanger. But black does not mean rust.

Either lack of refrigerant, stopped up metering device or capillary tube/s, or lack of air flow (due to bad blower motor, or dirty indoor coil) Good luck.

SANDRA!? You answered your own question! What is bad then? THE THERMOSTAT! You need a new one; $5-7 at Home Depot

If you need further help, reach me via phone at https://www.6ya.com/expert/steven_b77d19396bfe2249

1) Product manual has burner info page 11, maintenance 12, and troubleshoot flow charts starting page 17
Otherwise, Rheem does not post service manuals.
http://bostonheatingsupply.com/Rheem/Rheem%20Commerical%20Gas/Rheem_CommGas_Extreme_Use%20and%20Care%20Manual.pdf

2) Post question on pro water heater forum.
http://www.thetankatwaterheaterrescue.com/forums/forum3/

3) Is air intake clear? Is the burner sooted? Is the flame large and clear blue? Is the vent obstructed? Does air draft when blower activates?

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Ignitor is probably too fare up. Adjust it lower !

Depending on the specific setup, there should be a reset in the gas line. Either a push OR pull button.

in front

1) Copy following link:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

2) For tank-type gas:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#pilot
http://waterheatertimer.org/How-to-repair-Rheem-TRD.html

3) Add comment and say what you find so far.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7