I have cleaned all of the inside of grill because the burners will not light. I went over vent holes with wire brush but still won't light. What is the problem? What else should I do?

Yellow flame is blocked burner clean out with Air line ,or wire brush ,prick out burner holes .

if your sure the propane tank is full, and the valve is open, (counter clockwise, and the control knob is on? you should not only smell it after 20 seconds, but if you put your ear near the grill you should hear a sound like air leaking.If you hear nothing and smell nothing, good chance there is a blockage in the line, or the burner holes are filled with drippings. First off, get a wire brush and scrub the burners where you see the small holes that the flame normally comes out of, then try the grill again, if still nothing (and your 100% sure the tank is full, the tank is on, and the control knob is on high) you may need to start taking apart the grill, looking for a blockage, many times its below the control knob where you will see an adjustable screen, spider webs and such will get in there and block the flow. Remember to not do any of that with the tank on the grill, remove the tank first.;

The burner is lighting back to the injector on the gas control. 2 things burner out of postion or burner is blocked needs cleaning, you can remove this and clean with air line or small bottle brush.

Removing them from the grill and cleaning with a soft wire bristle brush. Then blow them out with a can of compressed air with a straw nozzle (like you clean your computer with). Blow from the inside out. Any holes that may remain clogged can be cleaned with a straight pin or unfolded safety pin. The pin should be he same size as the holes in the burners. While you're at it and since the burners will already be removed, check the burner orifices for clogs. These can be removed and blown out, too.

Happy Grilling!!

clean burner holes with wire brush real good... if one burner lites and the next lites,but the first burners flame drops-replace Regulator. Its the hose that connects your tank. tapping metal housing with plyiers the next time it does it will show the plastic wheel inside housing is stuck and cannot allow the gas to flow

There is probably a clog inside the burner tube. you will have to removwe the burner from the grill and run a bottle brush through the tube, or with garden hose, spray into tube for a minute then with tube opening facing down, spray through burner hole to rinse out. this should be done to all burners, yearly.

Clean the orifices and small holes with a needle or paper clip. Also clean each control valve by inserting pin into hole. Shake out any dust from the tubes. Use wire brush in some areas. Good luck!

Remove the burners and clean the inside of the burners with compressed air and or a small long bottle brush.
The burner holes have a rust scale buildup in them.

Try looking for webs back to where the burner tube meets the valve. Otherwise you need to remove burner tube to access back of valve to clean with a torch tip cleaner or compressed air, (remember to disconnect grill from gas source first) inside valve orifice.  Usually the back of valve can be removed with a wrench. Worst case you always get a new valve off internet if you can't resolve the plug. Hope this helps, good luck.  

I know on some grills you can use a tooth pick to clean out the tiny holes that are plugged.