Abstract: A process and apparatus is provided for the selective production of hot water and steam from a constantly operating heater and with the use of a water pump intermittently feeding a constant volume of water through a conduit toward the heater, the pump and the heater being operable at a first rate of pumping frequency and at a first level of temperature for the production of hot water at a first operating condition. A control arrangement is provided for establishing a second rate of pumping frequency at the pump less than the first rate and a second level of temperature at the heater greater than the first level for the production of steam at a second operating condition.