The answer to 'why is my faucet no hot water' is that the most common causes are a faulty water heater, a broken hot water supply line, or a problem with the faucet itself. This can result in no hot water coming out of the faucet, or just lukewarm water instead of hot.
Some common symptoms include the faucet only producing cold water, the water taking a long time to heat up, or the water never getting as hot as it used to. Potential solutions depend on the root cause, but may involve repairing or replacing the water heater, fixing a leak in the hot water line, or replacing the faucet cartridge or valve. If you're not comfortable troubleshooting and fixing the issue yourself, it's best to call a professional plumber to diagnose and repair the problem.