Rheem Criterion II calls for heat and sometimes works.
I have a Rheem Criterion II furnace. Some of the time when the thermostat calls for heat the furnace will work just fine. Other times I will hear the exhaust blower turn on and then the burner turn on and the about 5 seconds later go out. The OK light will then have a flashing about every 4 seconds. When this happens if I turn the thermostat off and then back on or open the door to the electronics and then close it to activate the switch the furnace will start back up again but sometime repeating the problem other times staying on. The filter is clean and the pressure switch is working when I tested it.