I recently bought a house with a gas water heater and am getting odd results. Sometimes, i have plenty of hot water, other times, i can only get luke warm water. It is not due to other sources of water consuption. The variablity holds true even when the dishwater, washining maching, etc. has not been in use (first thing in the morning, for instance). Is this normal for gas water heaters? What could cause this variable amount of hot water?