On propane barbecues the hose & regulator has a safety feature on it known as a QCC. This feature may have turned the propane flow down because it has been triggered. To correct this, simply turn off tank and the grill and the regulator will reset itself. Then when you turn on the tank again do it very, very slowly and only ¼ to ½ of a turn. Then turn the barbecue on. This should rectify the situation.
Your burner port holes may be blocked not allowing an even flame across the burner. To fix simply run a wire brush over port holes and poke out blocked holes using a needle or small thumb tack. Burner should be cleaned this way once or twice a year to allow even flame distribution.
If there is no flame or a high yellow flame your venturi tube may be blocked and would require removing burner from bbq and cleaning venturi tube with a venturi cleaning brush. Remember spiders are attracted to the smell of gas and may return. Make sure spider web guards are in place over the venturi tubes.
Seasoning Cast Iron Grid : Spread a thin coating of cooking oil ( Vegetable, Olive, Peanut, Canola, Sunflower) over entire surface of the cast iron grids with a paper towel. Be certain the entire surface, including all corners, has been coated thoroughly. DO NOT use salted fat such as margarine or butter. Never use non-stick sprays to season your grids, as they just don¹t work. They burn off at a really low heat and do not protect the grids well.
Preheat barbecue for 10 minutes on HIGH. Turn burners to MEDIUM with lid closed. Allow barbecue to heat for 30 minutes. Turn all burners to OFF. Leave cooking grids in barbecue until they are cool. Your cast iron grids are now ready to use.
Reseasoning: After each use the grids should be reseasoned by coating with a cooking oil, closing the lid and leaving the cast iron grids in the barbecue until it is cool.
Storage: When Barbecue is not in use for long periods of time, store Cast Iron Grids in a dry warm place.
Food drippings often come into contact with the hot flames of the burner, causing flare-up. Flare-up is normal, but excessive flare-ups are most often caused by a build up of grease catching fire. To avoid large flare-ups, or possible grease fires, it is best to keep the Flavor System clean. Briquettes usually by flipping them over periodically or scrapping the excess grease of them. A metal flavor system need to be scrapped clean using a wire brush or putty knife ( be careful of porcelain finishes if your grill has that style). Then do a burn off for 15 – 20 minutes heat of the burner will burn off any excess grease. Also, ensure that the bottom of the casting is kept clean of any grease or cooking debris, including your drip can/pan or pull out tray.