How to Light a Furnace Pilot Light

Quick Answer

If your furnace pilot light is out and you do not smell gas, start with simple checks: thermostat settings, blower compartment door, and air filter. If the pilot won't light or stay lit, call a licensed HVAC technician. Never attempt relighting if you smell gas or are unsure about your unit—gas leaks can cause explosions.

What Is a Pilot Light, and Why Does It Go Out?

Older gas furnaces (pre-2010) often have a standing pilot light—a small, continuously burning flame that ignites the main burners. A safety device called a thermocouple senses the flame and keeps the gas valve open. Common reasons a pilot goes out include drafts, a dirty pilot orifice, a failing thermocouple, or an interruption in the gas supply.

Safety Boundaries: What Homeowners Must NOT Do

• Never attempt to relight a pilot if you smell rotten eggs (gas). Evacuate and call 911.
• Do not tamper with gas valves beyond the furnace manufacturer’s labeled instructions.
• Do not try to clean or replace thermocouples, pilot assemblies, or gas controls—these are pro-only tasks involving combustion safety and may violate local codes.
• If you are uncertain about any step, stop and call a professional.

Safe Homeowner Checks Before Calling a Pro

Perform these no-tool checks before you schedule service. They may restore heat without a service call and will help the technician diagnose faster.

• Thermostat: Set to "Heat" mode and temperature at least 5°F above room temperature.
• Furnace power: Confirm the furnace switch (often a light switch near the unit) is ON.
• Blower door safety switch: Ensure the front blower compartment door is fully closed—a loose door cuts power.
• Air filter: A severely clogged filter can cause overheating and shutdown. Check and replace if dirty (see air filter replacement guide).
• Exhaust/intake: Look for snow, ice, or debris blocking the flue or PVC intake/vent pipes outdoors.
• Gas valve position: The shutoff valve near the furnace should be parallel to the pipe (ON). Do not force it.
• Sight glass: If your furnace has a small window, look for a blue pilot flame. No flame? The pilot is out.

When to Stop and Call a Pro

Contact a licensed HVAC contractor immediately if:

• You smell gas anywhere—evacuate and call 911.
• The pilot lights but goes out when you follow the manufacturer’s labeled procedure.
• The pilot flame appears yellow or orange (should be blue).
• You’ve relit the pilot more than once this season.
• Rust, soot, or water is around the furnace base.

What a Professional Does: Inspection and Service

A qualified technician will ensure the area is safe, check for gas leaks, clean the pilot orifice and thermocouple, test gas pressure, verify safety controls, and relight per the manufacturer’s specifications. Common repairs include thermocouple replacement, orifice cleaning, or addressing draft and venting issues.

Typical Costs to Fix a Pilot Light Problem

Service	Editorial Estimate Range	Notes
Diagnostic service call	$80–$200	Standard weekday; after-hours emergency may be higher.
Thermocouple replacement (part & labor)	$150–$400	Most common fix when pilot won’t stay lit.
Pilot assembly cleaning	$100–$250	Often part of a maintenance visit.
Gas valve or control replacement	$300–$700+	Requires professional calibration and testing.

Editorial estimates based on national averages. Actual prices vary by region, season, and equipment. Use our HVAC Cost Estimator for localized pricing.

Decision Tree: DIY Check vs. Professional Help

Click to expand step-by-step decision path

1. Smell gas? → Evacuate, call 911. Do not proceed.
2. No gas smell? Do safe checks: thermostat ON > room temp? blower door secure? filter clean?
3. Pilot out? If you are experienced and the furnace manual provides relighting steps, you may attempt—but we strongly recommend calling a pro.
4. Pilot lights but won’t stay when button is released: → Call pro (thermocouple/cleaning needed).
5. Furnace still no heat after pilot lit and main valve ON: → Call pro for ignition or gas valve diagnosis.

Tools & Calculators for Smart Decisions

Make informed choices with HVACDatabase’s interactive tools:

• Furnace Age Decoder – Decode your unit’s serial number to see its age.
• Repair or Replace Calculator – Weigh fixing your pilot issue vs. upgrading an old furnace.
• HVAC Cost Estimator – Get real-world price ranges for pilot light service in your area.
• Quote Checker – Upload a contractor’s quote for independent review.

Contractor Checklist: Questions to Ask Before Hiring

• “Are you licensed and insured for gas furnace work in my municipality?”
• “Can you provide a written estimate that breaks down diagnosis, parts, and labor?”
• “Do you perform a combustion analysis and safety check after the repair?”
• “What warranty do you offer on the part and your workmanship?”
• “How quickly can you respond for a no-heat call in cold weather?”

Find prescreened local pros with our Contractor Search or compare up to three using our Contractor Comparison Tool.

Local Market Considerations

Cold Climates (e.g., Chicago, Minneapolis): A pilot outage during subfreezing weather can lead to frozen pipes within hours. Prioritize emergency service and consider an annual maintenance plan. Find emergency HVAC help.
Older Homes: Drafty basements and uninsulated furnace rooms can blow out pilots. Adding weatherstripping and sealing may reduce outages. Also see our guide on radiant floor heating for whole‑home comfort.
Coastal/Humid Regions: Salt air and moisture accelerate thermocouple corrosion. Schedule a pre‑winter tune-up to clean and protect components.

FAQs

Can I relight the pilot myself?

We strongly advise against DIY relighting unless you are experienced, there is zero gas smell, and you faithfully follow the manufacturer’s labeled procedure. The safest choice is always to hire a licensed professional to eliminate explosion and carbon monoxide risks.

How much does it cost to fix a pilot that won’t stay lit?

Expect $150–$400 if a thermocouple replacement and cleaning are needed. Costs can rise to $300–$700+ if the gas valve or other controls are faulty. Get a detailed quote upfront.

Why does my pilot keep going out?

Common reasons: dirty pilot orifice (spiders, dust), failing thermocouple, drafts, or an intermittent gas supply. A pro can safely clean the assembly, test components, and identify the root cause.

Should I turn off the gas if the pilot is out?

Only if you smell gas—then shut off the main gas valve (if accessible) and leave immediately. Otherwise, the furnace’s safety system has already cut gas flow to the pilot. Setting the thermostat to OFF is sufficient.

When is it better to replace my furnace instead of repairing the pilot?

Use our repair vs. replace calculator. Generally, consider replacement if your furnace is over 15 years old, the repair estimate exceeds 50% of a new unit’s cost, and the AFUE is below 80%. High‑efficiency upgrades often qualify for utility rebates.

Methodology

Cost ranges are editorial estimates derived from HVACDatabase’s aggregated service pricing data, contractor surveys, and industry benchmarks (ACCA, PHCC). Actual costs vary by region, season, accessibility, and specific equipment. Our safety recommendations align with NFPA 54 (National Fuel Gas Code) and OEM guidelines. Always consult local codes and obtain multiple written quotes for your specific situation.

For a broader no‑heat checklist, see our full furnace troubleshooting guide.