If there is pressure in the tank and no alcohol flow to the burners the flash back valve is stuck closed. This valve is basicly a check valve to prevent reverse flow or an explosion. These valves should be located on the stove
copper tube at the joint where the flex hose attaches. Stove
alcohol contains a small amount of water that causes corrosion at this valve and in the small passage in each burner casting.
From the author of books on boat refrigeration.