There is no hot water in bath. Hot comes just for a second and then only cold water comes. Hot water comes in all other taps in the house.

If you have a one handled faucet the hot water inlet ports on the cartridge are clogged. Shut the water off, open up the valve and check and clean the ports. Before you button up take and turn the water back oin for a moment to flush out the supplies. Reassemble and test. Now let's address why the ports were clogged. Do you flush your heater out on a regular basis? If not let me show you how. For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white or yellow grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. God luck, Tom