Hot hose down side of tub in the blink of an eye cools to lukewarm? We live in a semi-old house, and surrounded by one bathroom (the...

We live in a semi-old house, and surrounded by one bathroom (the only full bath), we just get hot sea for 1-2 minutes, then it comes out single lukewarm. We can turn it off, walk to any other faucet or shower, and get hot dampen. Its like this every darkness when we try to give our son a tub? Does it sound resembling something that could be moderately easy/cheap to fix, or am I going to have to phone up a plumber?
Answers:    Just throwing this out there. Is it possible that the water-in and water-out lines are crossed on the hot wet heater? If thats the shield, Your cold refill sea is filling into the top and not to the bottom via the dip tube and your hot hose down is pulling from the bottom of the tank. Another problem along matching lines is that the dip tube is broken causeing hot water for awhile and consequently luke warm marine after that. (kind of a short circuit) The dip tube is supposed to take the cold reload water to the bottom of the reservoir while the hot water at the top of the container goes to the faucets. The hip bath may pull adequate volume to make this adjectives where as the other faucets don't.
Good luck

Mike
which bathroom have outside walls? draft from vent from attic or baseboards??