I have a state selct gas water heater. Recently basement flooded. Water got high enough to reach the diphragm but not the burner. Pilot will light but as soon as a demand is called for the gas will flare up and then go out. If I leave the combustion chamber door slightly ajar I can start the burner at high demand and it will stay lit. Starts a nice blue flame then slowly turns orange and then goes out? If the diaphragm got wet is there a way to fix it or do I have to replpace the tank?

Pull the entire assembly out and clean it all very well. There is a flame rod that will not work when dirty and that is one potential problem. It is a small rod with an insulator that goes in flame. It looks like a small platinum spark plug and is made just like one. Clean with fine sandpaper. Look at gas valve because one of the bleed orifices could be stopped up or partially blocked and the way yours is acting I think one is blocked. You can take it apart to fix it.