Originally Posted by Rastusann
We are hooked up to electric. Heater had worked just a week ago. When we turn on the heat, the fan kicks on and you can hear it click like it is trying to light. It does that 3 times and then kicks off.
Well, you did gain some information. The clicking sound you hear is the igniter attempting to light the burner. Often furnaces will attempt to light 3 times and then go into lockout.
The fact that you hear the furnace attempting to light indicates that the thermostat, sail switch and the high limit switch are working normally, however the flame sensor never detects a flame. So the issue could be the igniter itself (or its adjustment), the gas valve, the gas flow into the valve, or the circuit board that controls it all. It could also be wiring to any of these components.
If you cannot reach or see these components then you will most likely have to remove the furnace. I have done this myself and ran the entire system off of a car battery and propane bbq tank to test it.