I assume you checked the gas lines for blockage/restrictions.
You say you "even have an adapter and tried on a 20# bottle". Have you tried with a 16.4oz coleman bottle? If not give that a try. Sometimes the regulators on these things get a little finicky with the hoses.
If the 16.4 bottle works, regulated is confirmed good. Next step would be make sure burnrs are off, connect adapter hose-no bottle attached- then attach 20# bottle and open valve very slow, take a full minute. Sounds crazy, but I have had to do this firmly weber q200 because something was triggering the weber regulator to intermittently to shut down because it sensed a leak. The try lighting.
If the 16.4 bottle doesn't work, you need a regulator.
By the way, for me the weber self corrected after 2-3 uses when very slowly opening the tank.
2007 Chevy Duramax LMM/Allison
2012 Jay Flight 29QBH
2012 Jay Flight 26BH (Sold)