Replacing a Water Heater Pilot Light and
How to Light a Gas Water Heater

Learn how to light a gas water heater properly. A step-by-step guide to replacing a water heater pilot light. How does it work, and what to do when the pilot flame goes out.

A water heater pilot light or pilot flame is a small gas flame used to ignite the gas burner inside the water heater. This small flame is continually burning to light the burner when there is a call for heating and from the thermostat.

The gas burner assembly usually consists of the pilot burner, tubing, thermocouple, burner tube, and main burner; all of them in charge of lighting the pilot and the water heater. The gas valve is, of 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 light the burner even if there is no electrical power (power outage, for example).

The main disadvantage of the pilot flame is the design that makes it constantly burning, resulting in energy waste when the unit is not operating.

The second problem is with the flammable vapors coming from the flammable liquids (paint, gasoline) that can be potentially ignited unless the unit is turned off.

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

Today more and more gas appliances utilize electric ignition using the sparks (high voltage electrical arc) from the electrodes or hot surface.

How to light the pilot light – Step-by-step Instructions

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

The most common lightning system is a piezoelectric igniter system, consisted of the igniter button, an electrode, and a wire. The water heater pilot light is ignited by an electric spark generated when the igniter button is depressed. The spark gap distance measured from the electrode tip to a pilot is factory set to 0.125 inches and must 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.

Here is the step-by-step guide on lighting a hot water heater if the piezoelectric igniter ignites the pilot flame.

• Remove the outer door panel.
• Turn the temperature control to its lowest setting.
• Put the gas knob to the OFF position.
• Wait for a few minutes to clear out any accumulated gas.
• Turn the gas control knob to the 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 loud click.
• Continue to hold the button for up to one minute after the pilot light is lit 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 the gas control knob to the ON position.
• Set the thermostat to the desired temperature.

Also, check these instructions found in the article about different types of gas valves, it can help you understand the lighting process better.

Protection

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

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

The water heater is designed to automatically shut off if the pilot light is extinguished for any reason. Thanks to the safety devices, the gas will not keep coming out of the pilot light tube.

The thermocouple is one of these safety elements that prevents the gas from coming out. While sitting in the pilot flame, it can determine if the flame is present or not. The 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 and close the safety valve.

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

How to replace the water heater pilot light and tube assembly

• Turn off the gas supply to the water heater by putting the knob in the "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 the feedline.
• Follow the instruction located on the lighting instruction label to resume the operation.

Of course, there are other reasons for the pilot failure, and several are covered in the article - pilot light goes out due to improper venting.

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