Expert Guide to 22 Key Boiler Parts: Functions, Names & Diagram

A boiler is a highly sophisticated piece of equipment that is the backbone of many industrial and domestic heating applications. This closed vessel efficiently heats fluids to high temperatures without allowing them to boil, making it a safe and reliable energy source. Once heated, the fluid exits the boiler and is utilized for various purposes, including water heating, central heating, power generation, cooking, and sanitation. With its exceptional efficiency and flexibility, the boiler has become indispensable in many industries, powering various processes with heat energy. In this article, we will explore all the parts of a boiler with their functions & diagram.

Boiler Parts Diagram

Parts of a Boiler, Names, Functions & Diagram

Parts of Boiler Names

  • Burner
  • Combustion Chamber
  • Heat exchanger
  • Aquastats
  • Circulator pumps
  • Controls
  • Economizer
  • Air-preheater
  • Superheater
  • Exhaust stack
  • Deaerators/Condensers
  • Expansion Tank
  • Supply lines
  • Return lines
  • Backflow Valve
  • Safety Valve
  • Stop Valve
  • Blow off valve
  • Refractory
  • Manhole
  • Pressure Gauge

Boiler Parts


The function of the burner is to produce heat by combusting the fuel to heat the fluid. Air and fuel mixture comes into the burner, and the fire spark produces heat.

When we start the burner, the electronic system sends the signal to the fuel pump to supply the fuel. It comes from the fuel tank and passes through the filter to the nozzle.

Nozzle help to create a fine spray for the fuel to burn correctly. This heat is used to heat the fluid of the boiler system.

Combustion Chamber

It is a cast iron chamber where the combustion of the fuel happens. Cast iron is the best choice as it can withstand high temperatures and pressure.

The combustion chamber’s temperature is too high more than hundreds of degrees. Oil, kerosene, natural gas, and liquid propane are the typical boiler fuels.

Heat Exchanger

The heat exchanger is the bunch of pipes through which the fluid passes. When the combustion happens in the combustion chamber, heat transfers to the fluid through the heat exchanger.

In this process, fluid does not come in direct contact with the heat. The pipes of the heat exchanger get heat first and then fluid.

This fluid carries the heat from the combustion chamber to the other parts of the boiler. The heat exchange is of the copper due to its high thermal conductivity.


Aquastats send the correct signal to the burner to start and stop the heating by analyzing the temperature of the fluid inside the boiler. The control system of the boiler system decides to heat the boiler by analyzing the various parameters.

Circulator pumps

A circulator pump is a water-circulating pump of the boiler. It helps to distribute the hot water into the boiler radiator system’s various pipes for the boiler’s right functioning. It is necessary to have appropriate maintenance of the pump for better efficiency of the boiler performance.

The circulating pump supplies the hot water to the various outlets of the boiler in homes and offices.


The function of the controller is to control every piece of equipment and their working as per the requirement. It regulates the fuel supply, air-fuel mixture percentage, heat, water flow rate, pressure, the temperature of the boiler, and many more.

The control improves the safety of the boiler parts and increases their performance. It maintains the internal pressure and temperature of the boiler.

If the control system is damaged or not present in the boiler, measuring the temperature and pressure is difficult, which may cause a dangerous accident.


An economizer is a preheater that uses the heat of the flue gases to heat the fluid before entering into the boiler drum. It is placed in the exhaust system of the boiler system. It helps to increase the efficiency of the boiler.

There are three types of economizers.

  1. Gilled Tube Economizer: It has high optimum efficiency due to proper contact of gills with the tube.
  2. Coiled Tube: It requires less space and efficiently recovers the heat from the gases.
  3. Horizontal Finned Tube: In this type, carbon steel tunes are welded with horizontal fins to absorb more heat.


Its function is to increase the air temperature before entering the furnace. It places after the economizer. Flue gases pass to the air preheater through the economizer.

There are two types of air preheaters.

  1. Recuperative consists of multiple tubes inside the shell with baffle plates in between. A baffle plate helps to contact the flue gases with the tubes better. It has an inlet from the lower end.
  2. Regenerative consists of a closed matrix in which flue gases pass to the matrix to heat, and air pass to pick up the heat.


It is present in the path of the flue gases to use the heat of the flue gases to superheat the stem before entering into the turbine. Generally, steam generated in the boiler is wet or dry saturated.

It needs to pass from the superheater to convert into the superheated steam. It increases only the temperature of the steam.

There are three types of superheating.

  1. Convection- Steam takes the heat from the flue gases.
  2. Radiation- Steam takes the heat from the furnace radiation.
  3. Combined- It works on the above two types.

It helps to eliminate the erosion of the turbine blades and improves efficiency.

Exhaust Stack

It is a construction like a chimney of bricks or metal pipes. Its primary function is to expel exhaust gases safely into the atmosphere.

The Exhaust stack is constructed very safely due to leakage of these gases is dangerous for health. It is built so that high wind flow cannot downdraft the exhaust gases into the property.


It is only used in the stem boiler where fluid is in the stem form.

Expansion Tank

The function of the expansion tank is to protect the boiler from high pressure.

Supply lines

Supply lines are the pipes of the boiler which supply the hot water or steam to the distribution point of the boiler.

Return lines

When the stem becomes cold and transforms into water, return lines carry the water to the boiler for reheating.

Backflow Valve

It allows the fluid to flow in one direction only and restricts the backflow of the fluid.

Safety Valve

The function of the safety valve is to blow off the pressure inside the boiler when it exceeds its limit. It protects the boiler from the explosion by releasing excess pressure.

Stop Valve

It controls or stops the flow of stem or fluid into the steam pipes as required.

Blow Off Valve

It removes the water and steam from the boiler and is present on the bottom side. During the maintenance, we can use this valve.


It is a material that fills the gap or opening around the firebox.


It is a hole for entering the operator into the boiler during maintenance.

Pressure Gauge

The function of the pressure gauge is to measure the inside stem pressure of the boiler. Burdon’s pressure gauge is the most common type of pressure gauge.

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