The answer to 'why is my bathtub no hot water' is that there are several common causes, including a malfunctioning water heater, a problem with the plumbing system, or a blockage in the pipes. Symptoms may include lukewarm or cold water coming from the bathtub faucet, and the issue may affect other fixtures in the home as well.
Some potential solutions include checking the water heater's temperature setting, inspecting the plumbing for any leaks or blockages, and cleaning out the faucet aerator. However, if the problem persists or you're unsure of the cause, it's best to call a professional plumber to diagnose and fix the issue.