sounds like one of the safety shutoff devices in problematic
is there soot on anything near the burner, if so clean it off. other wise messing with them things is pretty dangerious.
these things are a danger when there working correctly, i hate to tell you how dangerious they are when malfunctioning. risk of fire, carbon monixide poisoning. double deadly
do you have a carbon monxide dector in the room? if not i would recomend .
i am not going to risk telloing you to do anything beyond cleaning the thing gently as they very dangerious as a simple internet search of "gas space heater accidents" will give you a thousand stories of death and burning with these devices
call your heating contractor and have something safe permently installed in that room for your safety and comfort