How Boilers Work

Boilers 101

Crash Course

A boiler is a closed vessel in which water is heated (not necessarily boiled). Originally used to power steam engines and ocean-going vessels, the traditional boiler was a bulky piece of machinery that was fueled by wood or coal and was difficult to clean. Firetube boilers, as they are now called, consisted of a tank or barrel of water with steel tubes running throughout. Fire would flow through the tubes and heat the water. Eventually, people realized the obvious inefficiencies in this design and created the watertube boiler, which is what we make here at Gasmaster.


Watertube boilers fill the tubes with water instead of flames and allow for higher pressure.

By condensing the water vapor that is produced during combustion and trapped in the flue gases they achieve a higher efficiency.

GIF explaining how boilers work
Water enters the boiler. Heat radiates outward heating the pipes as they get closer to the middle.

Throttle Mechanism

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 pre-purge periods are almost eliminated. This directly results in an increased useful life of the water heater and/or boiler and increased overall efficiency of the equipment.

Work Mechanism

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 burner. For as long as the set temperature is above that of the outlet water, the boiler/water heater operates at maximum output capacity.


Analog 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.