I have a 2 year old Gas Hot Water Heater in my house 50 gallon I believe. It runs out of water after about 5 minutes and the water does not seem as hot as it should be (It's turned to 3 on a max scale of 4 on the heater). The pilot light is on. Can you tell me what might cause the hot water to run out so fast. Nothing else is drawing the hot water.

Thanks,

Eric