The answer to 'bathtub no hot water' is that the most common causes are a faulty water heater, a problem with the bathtub's plumbing, or a blockage in the hot water line. Symptoms may include lukewarm or cold water coming from the bathtub faucet, and the water heater may not be heating the water to the proper temperature.
Some potential solutions include checking the water heater's thermostat and heating element, inspecting the bathtub's plumbing for any leaks or clogs, and flushing the hot water line to clear any blockages. If the issue persists, it's best to call a professional plumber to diagnose and repair the problem.