To set the temperature on a hot water heating boiler, first determine the type of unit you have. On an electric unit, turn off the power to the area, remove the metal plate to reveal the thermostat, and then use a screwdriver to adjust the thermostat setting. For an oil-powered unit, adjust the temperature by turning the knob on the side of the tank until the temperature is as desired.
If you have a hot water heater that runs on gas, find the temperature control, which is usually found on the bottom half of the unit or behind a metal plate, similar to an electric heater. Adjust the thermostat control a little bit at a time, testing the water temperature with each adjustment until it reaches the desired temperature. Some water heating boilers have two thermostats, and both need to be set to the same temperature.
Before you adjust the temperature on any type of unit, determine how much to change the settings. Run tap water until it becomes hot, and then fill a tall glass to the brim. Use a thermometer to test the water temperature. The standard temperature for the hot setting is at least 120 degrees Fahrenheit. Test the hot water temperature again after the adjustment to ensure it is correct.