I have Rheem heating and cooling system of the roof Model # RRA-A0030JK06X MANUFACTURED IN 1997.

The heater fan comes on and then the burner comes on and 30 sec or maybe a minute later the burner outs out. The red light on the control broad starts to blink 3 times.
I f shut the power off the unit it will some times come back on.

I have changed all the return air filters and the flame sensor.