Shutting off a hot water valve at the sink is easy, and everyone should be familiar with how to turn off the water supply lines in your home. The purpose of a supply valve is to divide the sink's hot water from the rest of the water system. If there is no separate hot water shut-off valve under the sink, the entire supply will have to be shut off temporarily.
Locate the valves under the sink. The hot water valve usually is located on the left.
Turn off the hot water line. Typically, turning clockwise will shut off the valve. If you are not sure which line is for the hot water, turn on the hot water at the faucet and then turn off one valve at a time until the hot water supply has been identified.
Locate your hot water heater if there are no valves under the sink. Turn off the hot water valve. Turning the hot water valve from here will turn the hot water off for the whole system.
Turn off the water, if necessary. Locate mainline water shutoff valve either outside or in the basement, and turn off the valve. This will turn off all water for the whole system.
If the valves are tight, you may need to use a crescent wrench, open end wrench or channel lock pliers to turn them.
When you are ready to turn on the water line, do it slowly to prevent the bursting of any seals. Watch for leaks. Because air can get into the line, once you open the valve, turn on the faucet until the water runs evenly.