What It Is
A pilot light is a small, continuously burning gas flame inside a gas water heater that serves as the ignition source for the main burner. When the thermostat calls for heat, the gas valve opens and the pilot ignites the burner flame. The pilot also heats a safety probe called the thermocouple, which keeps the gas valve open as long as the pilot is lit. If the pilot flame goes out, the thermocouple cools within seconds and the gas valve closes automatically - preventing unburned gas from accumulating.
What It Does
The pilot light performs two essential functions: it provides a ready ignition source for the burner, and it keeps the thermocouple heated so the safety system stays in the "allow gas flow" state. These two roles are inseparable - without the pilot flame, there is no ignition and no safety signal.
On older heaters (and many current standard models), the pilot burns continuously 24 hours a day. This is called a standing pilot. Some newer heaters use an electronic ignition system that only sparks when the burner is needed, which saves a small amount of gas. On electronic ignition units, there is no standing pilot flame to go out - instead, an electric igniter lights the burner directly when called for.
If you have a standing pilot unit and discover you have no hot water, the first thing to check is whether the pilot is lit. Many homeowners can safely relight it by following the instructions on the label affixed to the front of the gas control valve.
Where It Is Located
The pilot assembly is located inside the combustion chamber at the base of the water heater, near the main burner. On most units you can see the pilot flame through a small viewport window on the heater jacket, or by looking through the gap at the bottom where the access panel is removed. The pilot tube is a small copper or stainless line that branches off the gas control valve and runs to the pilot assembly.
How It Works
To light the pilot, the gas control valve is set to "Pilot" mode. Holding the knob down manually opens a small bypass gas flow to the pilot without opening the main valve. The piezo igniter (or a lighter) sparks to ignite the pilot flame. The flame heats the thermocouple tip, and after about 30 to 60 seconds the thermocouple generates enough voltage to hold the gas valve's safety solenoid open. At that point the knob can be released and set to "Hot" mode - the main valve is now able to open when heat is called for.
Common Problems or Signs of Failure
- Pilot will not light or stay lit after following relighting instructions - thermocouple may have failed
- Pilot lights but goes out after releasing the knob - thermocouple is not generating sufficient voltage
- Pilot flame is yellow or orange instead of blue - incomplete combustion; possible draft issue or dirty orifice
- Pilot keeps going out repeatedly over weeks or months - thermocouple nearing end of life
- No hot water and no pilot visible through viewport - pilot has simply gone out (most common cause)
Can a Homeowner Check It?
Yes - checking whether the pilot is lit is a reasonable first step for any homeowner. Use the viewport window or remove the lower access panel to look for the pilot flame. If it is out, you can attempt to relight it following the instructions on the gas control valve label. Read all the steps before starting and follow them in order.
- Look through the viewport or access panel opening to confirm whether the pilot flame is burning
- Read the relighting instructions on the label on the gas control valve before touching any controls
- Confirm there is no smell of gas before attempting to relight - if you smell gas, do not attempt relighting
- After relighting, confirm a blue flame is visible and the burner comes on when the thermostat calls for heat
If you smell natural gas, do not attempt relighting. Leave the area and call your gas utility's emergency line.
When to Call a Plumber
Call if the pilot will not stay lit after following the relighting procedure, if it goes out frequently, or if the pilot flame appears yellow or orange. These symptoms usually point to a failed or failing thermocouple, which a plumber can replace in a straightforward service call. Also call if you are not comfortable working near gas components - that is a completely reasonable choice.
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