Water Heater Pilot Assembly 101

Erin Trybulec • Dec 02, 2019

Article Originally Published December 2, 2019; Last Updated September 24, 2022

***DISCLAIMER: PLEASE REFER TO YOUR MANUFACTURER’S INSTALLATION MANUAL FOR INFORMATION REGARDING YOUR SPECIFIC MODEL. IF YOU ARE ATTEMPTING TO SERVICE YOUR OWN HEATER, PLEASE DO SO WITH CAUTION. THIS ARTICLE IS MEANT TO PROVIDE AN INFORMATIVE + EDUCATIONAL SUMMARY AND DOES NOT SUPERSEDE OFFICIAL ONSITE DIAGNOSIS/REPAIRS OR INFORMATION FROM YOUR UNIT'S MANUFACTURER.***

What is a pilot assembly?

The pilot assembly can only be found on a Natural Gas water heater or a LP water heater (Liquified Petroleum water heater). It typically consists of a pilot, ignitor, and thermocouple (or a thermopile which is multiple thermocouples built into a single part).

The pilot assembly connects the burner to the gas valve and is responsible for providing the pilot flame that lights the main burner. Without a pilot flame, a gas water heater will not produce hot water.


How does a pilot assembly work?

Let's Think of a Gas Stove Top:

First, you turn the knob on the front of the stove, setting the desired flame temperature. As you turn the knob, you will hear a quick clicking sound which is usually followed by a blue flame appearing around the burner. Internally, turning the knob triggered the pilot to spark, opening up the gas line. The combination of the spark, gas, and air produces the blue flame you see; the higher the desired temperature, the more gas is initially required to reach said temperature.


Let's Apply our Gas Stove Top Idea to a Gas Water Heater:

Gas appliances are generally very similar in their sequence of operations. A gas water heater compared to a gas stove is no exception: the water heater's gas valve has a knob or dial on the front (the gas knob) which can be used to control the temperature settings, also controlling whether any gas enters the unit through the gas line. Conventional gas valve models have a separate knob which can be used to spark the pilot's ignitor. Adjusting the knob by turning it on/off or setting the temperature will communicate to the desired temperature to the gas valve's thermostat. Please note that it is not recommended that you change the settings from those outlined in the manufacturer’s installation manual to reduce the risk of scalding.ļ»æļ»æļ»æļ»æļ»æļ»æļ»æļ»æļ»æ


When there is a demand for hot water, the gas valve's thermostat communicates with the pilot assembly. When the ignitor sparks, it ignites the pilot light, then the flame spreads to the main burner. The thermocouple or thermopile then maintains communication with the gas valve to ensure that the water heater is operating safely via electrical current. In the event that the pilot flame or pilot light goes out, the thermocouple will send a signal to close off the gas valve and gas supply because its outgoing electric current will decrease, indicating there is an issue.   

Where is the pilot located?

The pilot is located near the bottom of the unit, attached to the gas valve, through the burner door assembly, and to the bottom of the main burner. You cannot see the entire pilot directly from an outside view, but you may be able to see the silver pilot tube line and copper thermocouple or thermopile leading down from the gas valve inside the burner or manifold door assembly. You can see the water heater's burner door when you remove the panel (aka the jacket door) that covers it. Upon removal, you may see a red/orange circular grommet inserted into the burner door assembly. The grommet helps affix the pilot into place as half of its lines are inside the unit and half are outside, connected to the gas valve. Beyond the components of the pilot assembly, the burner door also contains the sight glass which allows you to see the burner chamber and the flame when the water heater is in operation.

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  • Power Vent Diagram showing pilot assembly

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Anatomy of a Water Heater Pilot Assembly

*Click images to enlarge*

Semi-electronic pilot contains gas supply line, ignitor, and thermocouple

Electronic pilot contains gas supply line and electronic ignitor

Water Heater Pilot Assembly Descriptions

Ignitor/Igniter | The ignitor is the “rod” that ignites the gas by creating a spark at its tip

Thermocouple | The thermocouple is a copper temperature sensor which communicates with the gas valve/gas line, allowing it to remain open or closed, depending on whether the pilot is lit

Burner Bracket | A bracket which helps the installer screw the pilot into place at the bottom of the burner assembly

Compression Fitting | This is the golden piece at the end of the pilot tube which secures the line of flex tube into the gas valve; it serves as a 

Grommet | The red/orange circular piece which “locks” the pilot into the manifold assembly

Manufacturer’s Label | This contains the pilot’s part number and is crucial if your pilot is in need of replacement 


What is the difference between pilots?

Depending on the age of your unit, you may have a semi-electronic or completely electronic pilot. In our labeled example photos, the first is a semi-electronic pilot assembly, with three lines: gas supply line, thermocouple, and ignitor that contains a gas valve connection. The second example is an electronic pilot, with a gas supply line and white wire with a black clip which is inserted into the gas valve. This type of pilot is completely controlled by the gas valve. The other main difference between pilots is the size; newer units tend to have an all-inclusive electronic pilot assembly. This means that the pilot assembly cannot be “parted out;” rather than only replacing the igniter or the thermocouple, the entire pilot would have to be replaced. An older water heater may have a pilot assembly whose thermocouple can be individually purchased. 

What causes water heater pilot assembly failure?

Pilots and gas valves are two of the mostly commonly malfunctioning parts on a gas water heater. They can last as long as your unit, but are prone to wear and tear from daily use, especially during the winter months. Pilots with a thermocouple are subject to wear from the constant ignition of the flame, which tends to turn the thermocouple's copper color to a grey/black color (see Anatomy of a water heater section).


Additional causes of pilot failure include:

  • Air in the gas line
  • A faulty gas valve
  • Loose wire connections
  • Blocked ventilation
  • Worn out or broken resistor
  • This is particularly common with older water heaters who have a resistored pilot assembly (especially part number 100109295)

Water Heater Pilot FAQs

  • When do pilots tend to fail?

    Water heater pilots tend to fail after extensive use when the thermocouple becomes worn out; our customers typically tend to see pilot failure within the first year of use in high use case scenarios, but pilots experiencing regular usage levels tend to last around 5+ years. Pilot failure occurs most frequently during the winter because water heaters often work harder when incoming water temperatures are lower. 

  • How much is a replacement pilot?

    Water heater pilots can cost anywhere from $20 to $250 for residential water heaters; the median cost is about $80.


    We stock a wide variety of pilot assemblies for A.O. Smith, Bradford White, and Rheem. Some of our most popular pilot assemblies include:

    • 100112330 | A.O. Smith Pilot Assembly Kit (Natural Gas) - for 300 Series Water Heaters
    • SP21058 | Pilot Assembly Replacement Kit
    • 415-47845-05 | Bradford White Icon NG Natural Gas Pilot Assembly

  • Can I replace the pilot on my own?

    We strongly advise that a qualified service professional replaces your water heater's pilot assembly because it requires touching the gas valve.

Need some assistance installing a new water heater pilot assembly or finding the correct water heater pilot assembly replacement part? Contact us today for more information about local water heater service!

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