open the top one and open the bottom one and close the one in the middle also check to make sure the propane tanks are full if so close them and bleed the gas from the line by turning on the stove burner then go open the tanks again very slowly and purge the gas line again by starting a stove burner and letting it run for a bit then relight the hot water tank if this does not fix then the thermostat which is attached to the outside of the hot water tank has either come loose or is bad from the factory could also be a bad control board