I have an oil burning hot water heater with a capacity of 30 gallons. My problem is that I cant take two showers in a row without running out of hat water. I replaced the shower head to a 2.5 gallon/minute head but that didnt help. I also tried turning the water temp on the aquastat to high. The water starts out plenty hot enough but just wont last. Could the water pressure entering the water heater be causing this problem? I dont know what else to try.Thanks, Tillio