Water Heater Burner Assembly

Gas burner inspection and cleaning

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How properly to maintain a water heater burner assembly and keep the efficiency and performance high. Find out how regular gas burner cleaning reduces the heating problems.

Storage or tank-type gas water heaters are the most popular devices for water heating in North America. One of the reasons for its popularity is the simple design, reliable and easy-to-use components. The main elements in the tank-type heaters are the gas control valve and gas burner assembly, so regular inspection will provide high performance and years of trouble-free work.

If these elements are not working or working with the reduced capacity, the odds are that you will experience uncomfortable shower or lack of hot water.

How water heater burner works

bradford white water heater burnerWhenever you open the tap, hot water leaves the tank from the upper section and at the same time cold water replaces it at the bottom of the tank.

Once the thermostat senses that water is below the set temperature, it sends the signal to the gas valve to open gas, and pilot light fires the water heater burner to heat the cold water. Even if you are not using hot water, if the temperature inside the tank drops below the pre-set temperature, the gas burner will come ON.

The most used way of lighting the gas burner is by standing pilot light, while other more advanced methods include electronic or spark ignition and hot surface.

Every water heater burner, either using natural gas or propane produces a carbon dioxide and water vapor, as the result of gas combustion. From the water heater burner and combustion chamber, combustion byproducts will, through the flue and chimney, leave the heater to the outdoors.

Most of the gas burners will burn the gas and heat the water with the efficiency of 60-70%, using the energy from the combustion chamber, while condensing water heaters, such as AO Smith Vertex, will steal the energy from the flue gases and increase the efficiency to 90% or more.

Burner assembly

Water heater burner assembly consists of several elements:

  • Main burner

  • Main burner orifice

  • Main burner gas supply tube

  • Pilot burner orifice

  • Pilot burner gas supply tube

  • Thermocouple as the safety element is used to determine is the pilot flame present or not, and will shut off the gas supply to the main gas burner if the flame is absent.

TCO or Thermal Cut Off switch is an integral part of the thermocouple, and it will shut off the pilot burner and main burner when activated. The element is activated when the temperature inside of the combustion chamber significantly increases. One of the reasons for the excessive temperature is due to the flammable vapor ignition.

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Gas burner is located in the combustion chamber, where, for the proper work should get sufficient supply of fresh air. If the oxygen is not available in the right amount, water heater burner will not burn the gas correctly, causing the following:

  • Sooting

  • Yellow flame

  • Carbon monoxide

  • Smell of burnt gas

If the wrong size of the orifice is installed, is dirty or the gas tube is unclean, the main burner flame will be too large or very small. If the burner flame floats and lifts off the port, the orifice might be too big, the pressure is high, cold drafts or the flue and vent system are blocked.

Black or red granules found on the main gas burner are symptoms of the condensation, when mild acid water is dripping, which corrodes the steel and makes a sizzling noise. In a case of the excessive condensation, water is running down the flue tube and onto the main burner, putting out the pilot flame. Keep in mind that condensation is common at the time of start-up after installation and due to cold incoming water.

Also, if the water heater is cleaned and flushed periodically this will prevent sediments and lime deposits to rise up to a level when it is hard for the gas burner to heat water.

How to inspect burner flames

Soft blue flame is the sign of the correct gas combustion. Use the viewport at the bottom of the water heater to inspect the burner flames, at least twice a year. If you see blue tips with yellow inner cones, it is still OK. If the flame is all yellow or with the blue and orange colors or there is sooting, something is wrong.

Gas burner cleaning

Every time you clean the water heater burner assembly the control knob on the gas valve has to be in the OFF position, and the main valve located beside the water heater also turned OFF.

  • Remove the outer door.

  • There are usually two screws holding the manifold/burner door assembly to the combustion chamber. Remove them.

  • Disconnect the gas valve, main burner and pilot feed line, thermocouple and pilot tube.

  • Remove the burner assembly from combustion chamber and burner from the burner assembly (it is usually secured by two screws).

  • Visually check the burner and burner ports for any damages and clean it if it is dirty or clogged; use hot water, soap and soft paint brush.

  • Clean the rest of the burner assembly elements, including pilot tube, flame arrestor, combustion chamber... You can also use compressed air (vacuum) to remove any deposits from the burner and its screen.

All gas-powered water heaters today are designed with the FVIR system, which reduces the risk of the accidental fires, when the flammable vapors enter the combustion chamber and are lit by the burner. Low NOx water heaters are becoming more and more popular as they are equipped with the environment-friendly gas burners that have reduced NOx emission. The perfect example is the Promax Ultra Low NOx water heater that utilizes Enhanced Green Choice gas burner.


If water heater burner assembly is properly maintained and serviced, it will provide clean and efficient gas combustion. The gas burner is working only when there is a call for heating, and as the safety precaution it won't ignite when the pilot is not lit, when the thermostat is set too low, there is a dirt in the gas, main burner or pilot line, lack of fresh air or due to the thermostat and thermocouple malfunction.

(All pictures are courtesy of Amazon.com)