The answer to 'sink no hot water' is that the most common causes are a failed water heater, a broken hot water supply line, or a problem with the sink's hot water valve or faucet. Symptoms include only cold water coming from the sink faucet and no hot water available anywhere else in the home. Solutions may involve repairing or replacing the water heater, fixing a broken pipe, or servicing or replacing the sink's hot water components.
In many cases, the cause can be diagnosed and repaired by a skilled DIY homeowner. However, for issues with the water heater or major plumbing work, it's best to call a professional plumber to ensure the problem is properly diagnosed and fixed safely and to code.