I have Rheem Criterion II (RGDG). It starts and the flame comes up and run for 1 or 2 minutes. Then the flame back up and trips the roll out limit switch. The gas shut down and the blower keep going until I shutdown the power to the furnace. I replace the air filter, that helps the flame ON time. Now it runs for 10 or 15 minuites. But still the flame back up and shut down the gas. Any idea what's wrong?

May be to high gas pressure or a stopped up heat exchanger. Go out side to the vent of your furnace and see if you have a rotten egg smell. This will let you know if you heat chamber is cloged

Thank you for your reply! I don't smell anything from the vent. I cleaned with a shop vac inside the flame area. But I cannot get inside the heat exchanger. How do I get access to this area?
I thought the filter helped, but when swich on the furnace today, it shut down after 1 minuite.