gas heater 101 please :)

I am having troubles with over head gas radiant heaters. I can get parts but calling a heater repair man is to expensive for simple stuff I should know my self. Doese any one know of a web site that has a good primer on gas radiat heaters, valves , pilot, ect. I need to bone up on this,Thanks

Well I tore into the heater and found dirty pilot tube , seems to work well now. Still would like to find a primer on these things to bone up one :)
Frrst cold spell of the year, got the weep system up to spec and lots of deicer ready . We do not use the floor heat here. to Expensive for gas. We just throw deicer around and tell people to be caerefull. If they want ice free car wash its down the street at the tunne :)