My heater Evcon Unit model DGAAo7oBDTB
Serial # WOB69557912 a forced air heater tries to start, it clicks but then turns off and doesn't start.

Do you ever see the glow plug "glow"? If not, check for voltage to the glow plug (hot surface igniter) when it should be glowing and if you have voltage (roughly 120v), but it never glows, you have a bad igniter. Replace it and you should be all set. If no voltage to igniter, let us know and we will take the next step. Oh, and is the draft inducer ever turning on? If not, forget about the glow plug and check for voltage to the draft inducer. Lots of option here, so lets take it one step at a time.