How Do I Relight My Furnace Pilot Light?

Relighting a furnace pilot light takes about ten minutes: turn the gas control knob to Off, wait five full minutes for gas to clear, switch it to Pilot, press and hold the knob, light the pilot with a long lighter, keep holding for 30–60 seconds so the thermocouple heats up, then turn the knob to On. If the pilot stays lit, set the thermostat and wait for the burners to fire.

One rule overrides everything below: if you smell gas at any point, stop immediately. Don’t light anything, don’t touch switches, leave the house, and call your gas company or 911 from outside. This guide is for older furnaces with a standing pilot (a small flame that burns continuously) — typical of furnaces built before roughly 2000. If your furnace is newer, it almost certainly uses electronic ignition with no pilot to relight, and this procedure doesn’t apply.

Standing pilot vs. electronic ignition: how to tell which you have

Confirm you actually have a standing pilot before you touch anything. If the gas valve inside the burner compartment is labeled Off / Pilot / On, and you can see (or remember seeing) a small blue flame burning continuously near the burners even when the heat is off, you have a standing pilot — typical of furnaces 20+ years old. If the valve only says On/Off and you hear a click-click-click or see an orange glow before the burners fire, you have electronic ignition — it relights itself every cycle and there’s no pilot to maintain. Ignition problems on those systems (igniter, flame sensor, gas supply) are a technician’s job.

Safety first: the gas smell protocol

Do this before you start, and repeat it at every step:

1. Sniff around the furnace and floor level. Utilities add a rotten-egg smell (mercaptan) to natural gas, and gas is heavier than air — check low.
2. If you smell gas, stop. Period. Don’t press the knob, don’t light a match, don’t flip any switch. Walk out, and call your gas company or 911 from outside your home.
3. Wait the full five minutes after turning the gas off. This clears accumulated gas from the chamber. Skipping the wait is how flash fires happen.
4. Use a long-reach lighter or long fireplace match — your hand should never be inside the burner area when the flame appears. Have a flashlight in your other hand so you can see the pilot assembly.

Also: relight the pilot only when you know why it went out. If it died after you turned the gas off for maintenance, that’s expected. If it went out on its own while gas was on, that suggests a failing thermocouple, dirty pilot orifice, or draft problem — relight once and watch it; if it won’t stay lit, see troubleshooting rather than relighting over and over.

The 6-step relight

Step 1: Turn the gas control knob to Off. The gas valve is inside the burner compartment (the lower access panel usually lifts off or unscrews). Rotate the knob to Off and wait five full minutes — time it on your phone.

Step 2: Locate the pilot assembly. Look inside the burner compartment for a small metal tube with a tiny nozzle — the pilot orifice — with a thin copper tube (the thermocouple) feeding it, sitting beside the main burners.

Step 3: Turn the knob to Pilot. Rotate the gas control knob from Off to Pilot. On some valves you press the knob in slightly while turning, or press a separate Reset button — check the label on the valve.

Step 4: Press and hold, then light the pilot. Press the knob (or reset button) down and hold it down — this manually opens the pilot gas. Bring your long lighter or fireplace match to the pilot orifice and light it.

Step 5: Hold for 30–60 seconds. Keep the knob pressed for at least 30 seconds, up to a minute. This heats the thermocouple (explained below), which is what keeps the pilot gas flowing after you let go. Release slowly. If the flame stays, continue. If it dies, repeat from Step 3 — but no more than three attempts.

Step 6: Turn the knob to On. Rotate to On, replace the access panel, and set your thermostat to call for heat. The pilot should light the main burners, and warm air should reach the vents within a few minutes. If the burners don’t fire despite a lit pilot, the gas valve or thermostat circuit needs a technician.

The thermocouple, explained in plain terms

The thermocouple is the furnace’s proof-of-flame — a thin copper tube, about pencil-lead thickness, sitting right in the pilot flame, with one job: shut off the pilot gas if the flame goes out.

Heat from the pilot flame generates a tiny electric current in the thermocouple, and that current holds the pilot gas valve open. Flame goes out → tip cools → current stops → valve snaps shut. That’s why a blown-out pilot doesn’t fill your house with gas — the thermocouple kills the supply automatically.

This is why Step 5’s waiting matters: the tip has to get hot enough to generate the holding current. Release too early and the valve closes, killing the pilot you just lit. A thermocouple that can’t generate a strong enough signal — from age or corrosion — is the number-one reason a pilot won’t stay lit.

A replacement thermocouple costs $5–$20 at a hardware store and is one of the few gas-component DIY jobs that’s genuinely safe: no gas-line disassembly, just unscrew the old one from the valve and slide the new tip into the pilot bracket. If you’re not comfortable working near the gas valve, a technician will do it as part of a service call ($100–$200).

Pilot won’t stay lit: the 3 causes and when to call a tech

If the pilot lights but dies the moment you release the knob (or dies repeatedly), it’s one of these three:

1. Worn-out thermocouple (most common). It degrades with heat cycles and produces a weaker holding signal until the valve won’t stay open. Clues: the pilot flame looks healthy and blue, but dies the instant you let go. Fix: replace the thermocouple ($5–$20 DIY; $100–$200 service call), and check the tip sits fully in the flame.

2. Dirty or partially blocked pilot orifice. Soot and corrosion narrow the tiny orifice over the years, producing a weak, yellow flame that doesn’t engulf the thermocouple tip. Fix: a technician cleans the orifice during a tune-up. Don’t try to ream it yourself with pins or wire — enlarging the hole changes the gas flow and makes things worse.

3. Downdraft at the flue. If the pilot flame flickers, lifts off, or gets blown out while everything else looks fine, air is blowing back down the flue — common after a flue cap blows off in a storm or when a nearby exhaust fan creates negative pressure. Clues: pilot goes out on windy days, or when the dryer or range hood runs. Fix: reinstall or replace the flue cap and have a tech check flue draft — a pro job, since bad draft also affects combustion safety.

When to call a technician:

• Three failed relight attempts (stop trying — repeated gas dumps into the chamber are dangerous)
• Pilot won’t stay lit after thermocouple replacement
• You smell gas at any point — gas company first, HVAC tech second
• The pilot flame is large, yellow, and sooty even after cleaning — possible gas-pressure issue
• The pilot goes out repeatedly and you can’t find an obvious cause
• The gas valve knob is stuck — never force it; valves can crack and leak

A clogged air filter is the other classic “furnace underperforms” cause on older units — How Do I Replace My Furnace Filter? covers it.

Fall maintenance for older furnaces

Standing-pilot furnaces are the least efficient systems still in common use — the pilot alone burns gas 24/7, roughly $10–$25/month wasted. If your furnace is 25+ years old, weigh each fall’s tune-up against replacement ($3,500–$7,500 installed), since a modern 90%+ AFUE unit can cut heating bills by a third or more.

Until then, this fall routine keeps an older furnace safe:

• Replace the air filter before heating season — restricted airflow is the top cause of overheating shutdowns on old units
• Book a professional tune-up ($80–$150): burner and pilot cleaning, thermocouple check, heat-exchanger inspection, and flue draft test
• Check the flue cap from outside — it should be present, undamaged, and clear of nests
• Test CO detectors — every home with a gas furnace needs them on each floor; replace any older than 7–10 years
• Keep the furnace room clear — combustion-air openings must stay unblocked

Safety warnings

Gas smell = full stop. Don’t light the pilot, don’t press the knob, don’t flip switches. Leave the house and call the gas company or 911 from outside.

Wait the full five minutes after turning the gas to Off. Lighting a pilot into a chamber that still holds accumulated gas causes a flash fire.

Never relight more than three times in a row. Repeated failures mean a component problem, and each attempt adds more unburned gas to the chamber.

Never force a stuck gas valve. A valve that won’t turn easily may be failing — forcing it can crack it and cause a leak. Call a technician.

Frequently asked questions

Why did my pilot light go out? The usual causes: a failing thermocouple, a dirty pilot orifice, a strong downdraft from the flue, or the gas being shut off for maintenance. If it went out on its own, treat it as a symptom — relight once, and call a tech if it dies again.

Is it dangerous if my pilot light goes out? Not by itself — the thermocouple automatically shuts off the pilot gas when the flame dies. The danger comes from relighting without the safety steps, especially if gas has accumulated. Follow the five-minute wait and the three-attempt limit.

Can I convert my furnace from a standing pilot to electronic ignition? Retrofit kits exist ($200–$500 installed), but on a 20+ year-old furnace they’re not worth it — the rest of the unit is near end of life. Put the money toward a new high-efficiency furnace instead.

How much does it cost to have a tech relight a pilot? Expect $100–$200 for a service call including thermocouple replacement and pilot cleaning. Bundled into a fall tune-up ($80–$150), that’s the best value.

My pilot stays lit but the burners won’t fire. What’s wrong? The pilot and the main burners use separate parts of the gas valve. If the pilot is steady but the burners don’t light when the thermostat calls for heat, suspect the main gas valve, the thermostat circuit, or a limit switch tripped — often from a clogged filter. If the burners fire but the air is lukewarm, see Why Is My Furnace Blowing Cold Air?. That’s a technician call either way.

Prevention tips

• Replace the furnace filter every 60–90 days in heating season — clogged filters cause the overheating shutdowns that get blamed on the pilot
• Get an annual fall tune-up on any furnace over 15 years old — burner and pilot cleaning plus a heat-exchanger inspection
• Keep the flue cap intact — wind-blown caps cause the downdrafts that kill pilots
• Don’t let the furnace room get stuffy — blocked combustion-air openings cause soot
• Know where the gas shutoff is and make sure everyone in the house knows too

When to call a pro

• Gas odor at any point — call the gas company first, then your HVAC tech
• Pilot won’t stay lit after three relight attempts
• Thermocouple replaced and pilot still dies
• Pilot flame is large, yellow, and sooty — possible gas-pressure problem
• Pilot repeatedly blows out on windy days — flue draft problem
• Gas valve knob is stuck — never force it
• Burners won’t fire even with a steady pilot
• Furnace is 20+ years old and the heat exchanger has never been inspected