Hey thanks all for the help,
@Bronco638 - just did that tonight to the sterling heater. Nothing really in the cap.
This is the second one, which I can keep the thermocouple going by hitting it with propane till red, but then it turns off, so I suspect this was an issue with the pilot venturi. BUT - This one does have a cracked heat exchanger *gasp*.
SO I think the sterling is prone to replacement.
The other heater, the Modine is still resisting efforts, it seems like its a gas valve - I'll probably convert the modine to intermittant start.
Anyone install radiant natural gas heaters? If I replace the 100000 btu sterling with a radiant, it seems like that would give me one forced air, one radiant, so the air temps could be controlled.
Anyone knowledgable in radiant gas heaters?