Performed Furnace warranty on 2020 AC Pro heater. Upon my diagnostic I found that the system was only heating up to about 68/69°. Further investigation showed that when I took the panels off of the burner doors I found that the burners were lighting on and off not consistently staying lit. Error 240 Was active indicating that there was a low flame current. Found that flame sensor was completely oxidizing covered in a green coating. Due to the condition of this flame sensor this needs to be swapped out to ensure that the flame is able to make contact with the sensor. A new sensor is being ordered and will be installed Once part is in. Customers completely aware and wants us to call Emily when part is ready. Upon departure system is not heating properly or staying lit need to install new sensor.