Normally you have to let the hot water run awhile in my bathroom to get the water hot. Now it is hot instantly which leads me to believe there is a leak somewhere; however, I looked at all the usual places... no leaks. I have a four year old water heater which seems to be operating properly. I have felt the floors where the pipes run and they are not hot. What do you think it could mean?

Is the water pressure the same? If there is a leak your pressure would go down. Has the thermis stat controls on the heater ben turnd up. Is the valve for cold water under the sink ben turn. Normally the water from the water heater cools whin sitting under the sink and you have to run the water to flush out the cool water. If the water is hot I wuld check the waterheater. But you are right in the fact that if the water for the hot side is constantly running it would cause the water to be hot quiker do to less could water in the line.

Is your plumbing under a slab? If so, a small leak could keep the water hot without losing much pressure. I would start by shutting the hot water tank off. Unfortunately most tanks lack a shut off on the outlet. You shouldn't shut the inlet off unless you have an expansion tank. If neither an expansion tank or outlet valve, shut the inlet off and open the bathroom hot. Let it set a couple of hours and then turn it off and the inlet on. Then see how long it takes to get warm water. If the delay is back, you do have a leak somewhere.