I have a hayward H300FDP that recently went into SF error code. I replaced the sensor and cleared that code. Then after firing and turning off 3 times in a row it goes to IF error code. I inspected all orifices on the burner and they are clear. I filled both propane tanks as I read these units can act funny when propane is low. I pulled the Flame Sensor and gave it a nice shine with steel wool. I was really expecting it to fire after that but it still has the same symptoms. The unit definitely fires and then shuts itself after about 3 seconds. It does this 3 times and goes to IF. Any other suggestions would be greatly appreciated.