Every Gasmaster boiler and water heater is equipped with a unique throttle mechanism. Within the operating range of each equipment, the throttle mechanism offers practically infinite modulation capability. While this can not eliminate the on/off cycles completely, it does reduce it by over 90%. Therefore, cold starts, and associated prepurge periods are almost eliminated. This directly results in increased useful life of the water heater and/or boiler, and increased overall efficiency of the equipment.

The unit's operation is governed by the desired outlet (hot water) temperature. Using a digital, high precision temperature controller, the owner will identify the required hot water temperature. A temperature sensor installed on the boiler/water heater outlet manifold continuously measures the outlet water temperature. A servomotor controlling the gas butterfly valve and the air damper (by means of a variable profile cam mechanism) allows for throttling of the air/gas mixture flowing into the Riello burner. For as long as the set temperature is above that of the outlet water, the boiler/water heater operates at maximum output capacity. Analogue output signals from the temperature sensor are sent to the temperature controller, which in turn sends corresponding signals to the servomotor. This throttles the flow of gas and combustion air in the gas butterfly valve and the air damper. Therefore, the appropriate volume of air/gas mixture flows into the burner, allowing for almost perfect air/gas mass, and volume ratios. As the outlet temperature approaches the set temperature, the air/gas mixture flow is gradually reduced by the servomotor (connected to the gas butterfly valve and the air damper). This results in the corresponding gradual decrease in the unit's capacity. Thus the throttle system allows for optimum continuous operation of the boiler, significantly reducing on/off cycles. The said system offers the user almost infinite modulating capacity within the boiler/water heater operating range.