My natural gas wall heater won't come on. Photos at

http://homepage.smc.edu/morgan_david/wallheater/

The pilot is lit. It was last turned on in July. Not having been used
since, cranking up the thermostat dial no longer fires it up. I had a
stove that would not let gas flow unless a certain detector near the
pilot got hot enough to "know" that a pilot was there to ignite the
gas. I wonder if these heaters have a similar defeat mechanism that
could be my problem (can't see it if so)? Or what other causes should
I considerr?

Is this something that can be fixed on a do-it-yourself basis or is
calling a pro recommended?