Water Heater Pilot Light
Lighting a Gas Water Heater

Replacing a pilot light

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This article will lead your through the useful information about the pilot, its role in water heating, how to light the pilot light, replacing, what to do when the pilot flame goes out and so on.

Water heater pilot light or pilot flame is a small gas flame that is used to ignite gas burner inside the water heater. This small flame is kept alight constantly so it can light the burner when there is a call.

The gas burner assembly is usually consisted of the pilot burner, tubing, thermocouple, burner tube and the main burner; all of them in charge for lighting the pilot and the water heater. Gas valve is off course the heart in this burning operation.

The main advantage of water heater pilot light over other alternatives is its independence of the electrical system, as it can still light the burner if there is no electrical power.

The main disadvantage of the pilot flame is its design that makes it constantly lit, resulting in energy waste when it doesn't heat the water. The second problem is with the flammable vapors coming from the flammable liquids that can be potentially ignited, unless the unit is turned off.

Due to the high concentration vapor problem many water heaters are equipped with FVIR system to shut off the gas supply to the burner and pilot, preventing the ignition of vapors in the area.

Today more and more gas appliances utilize the sparks (high voltage electrical arc) from electrodes to ignite the gas or hot surface vs. the old fashion way when match was used.

How to light the pilot light - Instructions

Based on the different gas control valve manufacturers, lightning instructions are slightly different.

water heater pilot lightThe most common lightning system is piezoelectric igniter system, consisted of the igniter button, electrode and wire. The water heater pilot light is ignited by an electric spark, generated when the igniter button is pressed. Spark gap distance measured from electrode tip to pilot is factory set to 0.125 inch and has to be maintained for successful lighting.

How to check the piezo igniter... check if the spark is present when the button is depressed fully. Use a sight glass window while viewing the pilot assembly to see the action, if it is present.

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Here is the step-by-step guide how to light a hot water heater if the pilot flame is lit by the piezoelectric igniter:

  • Remove the outer door panel

  • Turn the temperature control to its lowest setting

  • Put the gas knob to the OFF position

  • Wait for ten minutes to clear out any accumulated gas

  • Turn the gas control knob to pilot position (Robertshaw Gas Valve)

  • Depress and hold down the pilot set button or gas control knob to let the gas flow to the pilot burner only.

  • Manually ignite this pilot gas using the piezo igniter button by depressing the igniter until you hear a load click.

  • Continue to hold the button for up to one minute after the pilot light is lit, in order to let the flame heat the thermocouple and generate sufficient voltage to the gas valve.

  • Release the knob and it should pop back up.

  • Turn gas control knob to ON position.

  • Set thermostat to the desired temperature.

Also check these instructions found in the article about different types of gas valves, it helps in better understanding the lighting process.

If the knob does not pop up when released or pilot will not stay lit after several tries, turn the gas control knob to OFF position or the main gas valve and call service technician.

Air may be present in the gas line and could prevent the pilot from lightning on initial start-up. Gas line should be purged of air by qualified person.

Water heater is designed to automatically shut-off if the pilot light is extinguished for any reason. Thanks to the safety devices the gas would not keep coming out of the pilot light tube.

Thermocouple is one of these safety elements that prevents the gas from coming out. Sitting in the pilot flame it is used to determine if the flame is present. Thermocouple will send the electrical signal to the gas valve to shut off the gas supply to the pilot and main burner if the flame is absent. If the light is extinguished it can take up to 3 min for the thermocouple to cool sufficiently to close the safety valve.

To re-light the water heater pilot light, you have to manually push the button to open the gas valve. Then you light the pilot light and wait for up to 60 sec for thermocouple to heat up. Once it is hot, the thermocouple will generate the electricity that will hold the valve in open position. Then you can release the button.

The normal voltage for a properly working thermocouple is between 20 and 30 mv and when installing make the base flush with the base of the pilot bracket.

Replacing the water heater pilot light and tube assembly

  • Turn off the gas supply to the water heater by putting the knob to "OFF" position.

  • Set the temperature dial on the gas control valve and thermostat to the lowest setting.

  • Remove the door panel.

  • Remove the screws that are securing the manifold assembly to the combustion chamber.

  • Disconnect the thermocouple, the tube, igniter wire, thermal switch and manifold tube and push them slightly down to release them.

  • Remove the manifold assembly and release the burner.

  • Remove the pilot tube from the pilot bracket.

  • Using the old pilot tube assembly as a guide, bend the new tube and thermocouple to match the old ones.

  • Route the new pilot tube, thermocouple and igniter wire through the manifold assembly.

  • Bring everything back in reverse order, secure the screws, re-install burner assembly and connect feedline.

  • Follow the instruction located on the lighting instruction label to resume the operation how to light the water heater pilot light.

Find out more information why pilot light goes out due to improper venting.

water heaters

(All pictures are courtesy of Amazon.com)