I have a Tempstar model # nugk100dh08 furnace. I am trying to clean off the end of the flame sensor. Do I need to take the ignitor/sensor unit off? If so, I see that it has 2 screws on top of the unit. Do I just remove those and it drops down so I can clean? The problem I was having was the flame came on then would go out after 5-10 seconds. I reached up and cleaned the end of the sensor with finger. It is currently working and I see where the end of the sensor is caked with debris. Thanks for your help.