gas wallheater, no flow (thermostat?)

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?
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