The answer to 'why is my shower no hot water' is that there could be several common causes, including a malfunctioning water heater, a problem with the shower mixing valve, or a blockage in the water supply line. Symptoms may include lukewarm or cold water coming from the shower, and the issue may be isolated to just the shower or affect the whole home's hot water.
Some potential solutions you can try yourself include checking the water heater's temperature setting, cleaning the shower head, or troubleshooting the mixing valve. However, if the problem persists or you're not comfortable making repairs, it's best to call a professional plumber to diagnose and fix the issue properly.