Heaters
I would suggest checking the board (electrical board remove it and take to dealer and they can check it), limit switch (will shut off gas if too hot) and maybe the lp release fly (sorry, can't remember the name this) by the fan (if it is stuck, it will not allow lp to go to the burner. Also, make sure you check to see that there is no debre/dirt/rust, etc., in the burner (it will clog the burner).
I'm in the process of doing the same thing to my furnace (it quit in Feb while in Texas...tries to light but won't, just clicks). It is normal for the fan to come on the blow out any residual fumes in the system prior to the lighting of the burner.