The unit is not producing any hot water. Your pilot light may be out. Follow the instructions on the tank for relighting the pilot, or call your local gas company who will relight it for free! Water heater is not producing enough hot water. If the water heater runs out of hot water too quickly, increase the temperature on the water heater thermostat. If the temperature is set on the highest setting, ... Water heater makes a rumbling or clanking noise. Chances are this is related to sediment build up. A flush of the water heater may be all that is required.