The answer to 'bathtub no hot water' is that the most common causes are a malfunctioning water heater, a problem with the hot water supply line, or a clogged faucet. Symptoms include no hot water coming from the bathtub faucet, lukewarm water, or water that quickly turns cold. Solutions can include checking the water heater temperature setting, inspecting the hot water supply line for leaks or clogs, and cleaning the bathtub faucet aerator.
If the issue is with the water heater, you may be able to adjust the temperature setting yourself. However, more complex problems with the water heater or hot water supply system will likely require a professional plumber to diagnose and repair. Attempting to work on these components without proper training and equipment can be dangerous. For your safety, it's best to call a licensed plumber if you are unable to easily resolve the problem.