Rinnai Universal Temperature Controller Suit Continuous Flow Hot Water Systems MC601QA. Simply set the water controller at your desired temperature, and then turn on the hot tap. There’s no need to add any cold water to achieve your desired temperature. Water controllers allow precise temperature control by the user. When used correctly, the hot water unit will deliver the selected temperature, even when the water flow is varied, or more than one tap is in use. Each water controller can be individually programmed, however the water heater can only deliver one set temperature at any time.