The answer to 'why is my sink no hot water' is that there are a few common causes, including a faulty water heater, a clogged hot water line, or a problem with the sink's hot water valve. Symptoms may include no hot water coming out of the tap, lukewarm water, or water that quickly goes cold.
To troubleshoot, first check your water heater to ensure it is turned on and set to the proper temperature. If the heater is working, the issue may be a clogged or damaged hot water line leading to the sink. You can try flushing the line or inspecting it for blockages. If the issue is with the sink's hot water valve, you may need to replace the valve or call a plumber for repair.