The heater lights up and the fan motors turn on, I can see all burners are lit but the heater does not go to the next step of blowing the hot air through the ducks it turns of and the timer led flashes twice and that indicates a primary limit circuit open error. This heater is 16 years old and in the past I have replaced the main controller board and the fan that you can see when you open the cover. Sorry I do not know the terminology.