How do I light or relight a furnace pilot light? Safety first

What a pilot light is, and whether your furnace has one

A pilot light is a small gas flame that stays lit all the time. Carrier, a furnace maker, describes it as a flame that ignites the main burner in older gas furnaces.

Carrier says pilot lights are found in older gas furnaces made before the mid-1990s. Bryant, another maker, says a furnace made after the mid-1990s almost certainly uses electronic ignition.

Carrier gives a hot surface igniter or an intermittent pilot as examples of electronic ignition.

Carrier gives a simple way to tell. If a small, continuously burning flame is visible inside the furnace access panel, the furnace has a pilot light. If there is no standing flame and the furnace has a control board, it likely has electronic ignition. If your furnace has no pilot, a guide to relighting one does not apply, and our guide on a furnace that won't ignite is the better fit.

How the pilot keeps gas from building up

The pilot does not work alone. Carrier says a safety device called a thermocouple checks whether the pilot is burning. If it goes out, the thermocouple shuts off the gas supply to prevent dangerous gas buildup. Carrier says a thermocouple generates a small electrical current when the pilot flame heats it.

That current tells the gas valve to stay open. Carrier says that if the pilot goes out, the current stops and the gas valve closes on its own. Carrier calls a thermopile a more powerful version of the thermocouple.

Peoples Gas, a natural gas utility, says the same thing in plain terms. Most natural gas appliances have safety valves that shut off the gas automatically if the pilot light goes out. Carrier adds that a furnace with a standing pilot cannot make heat without it.

Why a pilot light goes out

Carrier says a pilot can go out for reasons that range from minor airflow issues to faulty parts. Its list includes drafts or air currents. It also lists a dirty or clogged pilot orifice.

The other causes on Carrier's list are a faulty thermocouple, low gas pressure, and a gas valve that is not working right. Bryant says a pilot that won't stay lit can point to a problem with a safety sensor, the gas valve, or another part.

How often it happens matters. Carrier says a working pilot should stay lit all through the heating season. It says an occasional outage from a strong draft may be normal. A pilot that goes out more than once or twice a season usually signals a problem that should be inspected.

Why this guide does not give lighting steps

Bryant recommends following the instructions on your furnace before attempting to relight a pilot. Carrier also says to always follow the maker's instructions for your specific furnace.

We do not repeat the lighting steps here, and that is on purpose. On this site, gas and combustion work goes to a licensed contractor.

Peoples Gas points the same way. On its Storm Safety page, it says to contact a licensed plumber or qualified appliance service contractor if you have questions or trouble relighting pilot lights. It also says to always check the appliance operating manual before lighting burners by hand.

Carrier lists the times to stop and call a professional. They include a gas smell at any point, a pilot that keeps going out after relighting, and a yellow, weak or irregular flame. They also include unusual noises after relighting, or feeling unsure of any step. Carrier says that if the pilot light won't stay lit after two or three attempts, stop and contact a licensed HVAC technician.

Gas smell, flame color and carbon monoxide

Carrier and Bryant both say not to relight the pilot if you smell gas. Peoples Gas says to get everyone away from the area or out of the building immediately, report the situation to 911 and then call its 24/7 hotline.

Peoples Gas also says not to do anything that might cause a spark. That includes turning any electrical or battery-operated device on or off. Do not try to find or stop the leak, and do not go back inside until the utility gives the all-clear.

Natural gas has no smell of its own. Peoples Gas warns not to rely on sense of smell alone to detect natural gas.

Carrier says a healthy pilot burns as a steady blue flame with a small yellow tip. Carrier says a mostly yellow or orange flame indicates incomplete combustion. Carrier says that should be handled by a professional.

Carbon monoxide, written CO, is the other concern. The Centers for Disease Control and Prevention (CDC) says gas furnaces produce CO and calls it an invisible, odorless poison gas. The CDC says to install battery-operated or battery back-up CO detectors near every sleeping area in your home. See our guide to carbon monoxide detector placement.

Gas heating in Florida homes

A U.S. Energy Information Administration (EIA) brief based on 2009 survey data says Florida residents use space heating equipment much less than people in other states.

The CDC says to have gas heating systems serviced by a qualified technician every year. Our heating tune-up guide covers that visit.

Storms are the other Florida case. Peoples Gas says gas appliances that may have been flooded or damaged in a storm should be inspected and serviced by a qualified plumber or appliance service contractor first. Peoples Gas says that during restoration, a gas technician may need to access the appliances in your home. Peoples Gas says to always ask to see an ID before letting anyone in.