Pilot Light Out or Furnace Won't Ignite?

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A gas heater cannot make heat without a flame, and the flame has to start somewhere. Depending on its age, your furnace or wall heater lights its burners from a small pilot flame that burns all the time, a pilot that lights only when needed, or a glowing electric igniter. Each fails in its own way, and only one of them is something a homeowner should ever relight. This page helps you work out which kind you have, what you can safely do, and when to leave it alone.

This guide is part of our Bay Area Winter Heating Help Center. If you are not yet sure the problem is ignition, start with the no-heat checklist.

Which ignition does your heater have?

The label on the inside of the burner door, or the rating plate, usually names the ignition system. If you can see a knob that says PILOT, you have a standing pilot.

Standing pilots: why they go out

A standing pilot does two jobs. It lights the burners, and it heats a thermocouple (or on some heaters a thermopile) that produces a tiny electric current telling the gas valve "the pilot is lit, it is safe to open". When the pilot goes out, the thermocouple cools and the valve shuts all gas off. That is a safety feature working, not a gas leak.

Common reasons a pilot goes out:

• Drafts. A window or door open near a wall heater, wind down a vent on a stormy night, or a floor furnace grate in a drafty hallway.
• A dirty pilot. Dust and spider webs clog the tiny pilot orifice over a long, warm summer. The flame goes weak and yellow and no longer wraps the thermocouple properly.
• A worn thermocouple. The pilot lights but goes out as soon as you let go of the knob. It is one of the most common standing-pilot repairs.
• A gas interruption. After PG&E work, a meter shutoff or a fumigation, every pilot in the house goes out at once.

Relighting a standing pilot safely

Only relight if you do not smell gas and the appliance has instructions for it. Every model differs slightly, so the label on your appliance wins over anything written here. The general sequence:

1. Turn the gas control to OFF and wait. PG&E's guidance is to shut the gas off at the appliance and "always wait five minutes to let gas disperse before trying to relight" (PG&E gas safety). If you smell gas at any point, stop and leave.
2. Turn the knob to PILOT and press it down (or press the separate reset button). This lets a small amount of gas reach the pilot only.
3. Light the pilot with the built-in push-button igniter, or a long lighter if the label says to, while keeping the knob pressed.
4. Keep holding for 30 to 60 seconds (or as the label says) so the thermocouple heats up, then release slowly. The pilot should stay lit.
5. Turn the knob to ON, replace any covers, and set the thermostat to call for heat. The burners should light cleanly from the pilot.

PG&E will relight pilots for free

Many Bay Area homeowners do not know this. PG&E says it "offers free safety inspections and gas pilot relight appointments" (PG&E help center). The service is open to PG&E's single-family and multifamily residential gas customers, and you book it online at pge.com/appt under Service Requests (PG&E pilot light service). PG&E also runs a winter gas safety campaign that promotes this free appliance inspection and relight program (PG&E 2026 Gas Safety Plan).

Book PG&E if you are uncomfortable relighting, if every pilot in the house went out after a gas interruption, or if you want an older wall heater or floor furnace looked at before winter. PG&E's visit is a safety check and relight, not a repair. If their technician finds a worn part or tags an appliance as unsafe, that is when you call a heating contractor.

Intermittent pilots: ticking with no flame

With an intermittent pilot, the control sends a rapid spark to light a pilot, proves the pilot flame with a sensing rod, then opens the main valve. Typical failures:

• Ticking, no pilot: a clogged pilot orifice, no gas to the furnace, a cracked spark electrode or a pilot valve that will not open.
• Pilot lights, burners never follow: the control is not sensing the pilot flame, usually a dirty or worn sensor or a weak pilot.
• Ticking that never stops, even when the burners are lit: a sensing or control board fault.

None of these are homeowner repairs. Turn the thermostat down so the system stops trying, and call.

Hot surface igniters and flame sensors

Newer furnaces light with a hot surface igniter, a small ceramic element that glows bright orange. It is brittle and wears out with heat cycles. When it fails, you hear the inducer fan start, wait for a glow that never comes, and the furnace retries a few times, then locks out.

If the burners do light but go out within a few seconds, the usual cause is the flame sensor, a thin metal rod in the flame. Lennox explains that it senses the presence of flame at the burner, and that a dirty flame sensor "will shut off the gas valve and the furnace, which prevents natural gas accumulations that could cause a fire" (Lennox). A sensor with a light coating can often be cleaned; one that is cracked or badly corroded is replaced. When the sensor is only borderline, the furnace may start some days and not others, or run short cycles, which our short cycling guide covers.

We do not recommend cleaning a flame sensor or touching an igniter yourself. The igniter cracks if touched or bumped, the sensor is inside the burner compartment, and a small wiring or reassembly mistake on a gas appliance matters.

When ignition trouble is really a safety warning

Some symptoms point beyond a worn part:

• A loud boom or whoosh when the burners light (delayed ignition). Gas is building up before it lights. Turn the heater off and call.
• Flames that roll out of the burner area, scorch marks on the cabinet, or melted wiring near the burners.
• A yellow, floppy flame or soot around a wall heater or floor furnace grille.
• A pilot that keeps blowing out on an older wall or floor furnace with no draft you can find, which can mean a venting problem.

Any of these can go with carbon monoxide. PG&E advises turning off the appliance you suspect if it is safe to do so, getting out, and calling 9-1-1 if anyone has symptoms (PG&E). The California Department of Public Health notes that CO deaths occur most often in the cold winter months and recommends having a qualified technician inspect your furnace every year (CDPH). Our post on the hidden dangers of old heaters explains why older units deserve extra attention, and our wall and floor furnace guide covers those heaters in detail.

What a technician checks

For a standing pilot, we check gas pressure, clean or replace the pilot assembly, test the thermocouple's output with a meter and replace it if it is weak, and look at venting and draft. For electronic ignition, we watch the full sequence, measure the igniter's resistance, read the flame signal from the sensor, check the gas valve and read the control board's fault history. We will tell you plainly when an old heater is no longer worth repairing. For typical price ranges, see our Bay Area furnace repair cost guide, and for the bigger picture on no-start problems, why your furnace won't turn on. Every repair carries our 1-year parts and labor warranty.

Book an ignition or pilot repair

Frequently asked questions

Written and reviewed by Jim McKinny, owner of Cool Aid Air Conditioning & Refrigeration — California C-20 and C-38 licensed, EPA Universal certified, second generation of a family business serving the Bay Area since 1966. Every job we complete is backed by our 1-year parts & labor warranty.