We have a 30,000 btu vent free propane wall unit(ceramic) at camp. It got a little chilly last weekend at night so I set it up on low. In the middle of the night I awoke to a very strong smell of propane. (upstairs) heater is on main level. I shut it off and aired out the place. Tested it the next day with doors and windows open. It seams like when its getting ready to cycle it puts out too much gas. But, It does not go POOFF when the bricks start glowing. I put a new regulator and hose on it last winter. (We use a 100lb tank for fuel). I don't know what to check next. I know I am afraid to use it.
You have dust in the grids and the orifices.Compressed air will get it out.Buy a few cans of the dry air for computers,remove the lower panel and blow out the orifices.Then blow out the grids with it.You may be able to shop vac it out but if you try be gentle near the grids.If you clean it regular I may be wrong.Blow off the thermocouple too.If you don't the pilot may go out.There is an orifice in the pilot also.
I have 5 vent free heaters in my house and 1 in my milk house.Every fall before I light em I give em a thorough cleanin and several times durin the cold season.Mine are natural gas but the principals the same.I betcha your pilot orifice jet is full of lint.