I called for a friend's house who had a heater that would blow cold air out for a bit and then immediately shut off. The temperature would not rise at all. It was set at 65 to 68, but the temperature would stay from 58 to 63 depending on the day.
I called Nevada Residential Services, they came, found that the problem was the flame sensor. I could not make the decision for my friend, so i said i would have to let my friend call them back on it. They said that since it was such a small part, that they would just clean it for free. Within 10 minutes, I could feel the heat coming out of the vents