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.
Water heater pilot light or pilot flame is a small gas flame that is used to ignite the gas burner inside the water heater. This small flame is kept burning constantly so it can 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 the 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 burning constantly, resulting in the 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 the electric ignition using the sparks (high voltage electrical arc) from the electrodes or hot surface.
Based on the different gas control valve manufacturers, lightning instructions are slightly different.
The most common lightning system is 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 has to be maintained for the 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 how to light a hot water heater if the pilot flame is lit by the piezoelectric igniter:
Also, check these instructions found in the article about different types of gas valves, it can help you understand the lighting process better.
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 contact the service technician.
The 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 the 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. Sitting in the pilot flame it is used to 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 manually to push the button to open the gas valve. 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 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.
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.