You hear the click.
You see the flame.
You feel hopeful.
Then—click. Silence. Cold air again.
When a furnace ignites briefly and shuts down, it’s not being dramatic. It’s doing exactly what it was designed to do: protect your home from unsafe combustion.
80,000 BTU 96% AFUE Upflow/Horizontal Single Stage Goodman Gas Furnace - GR9S960803BN
The good news?
This problem almost always points to a specific, diagnosable cause—and many of them are straightforward to identify.
Let’s walk through it the Savvy way: calm, methodical, and smart.
🧠 What “Lights Then Dies” Actually Means
When a furnace lights but shuts down shortly after, it usually means:
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Gas ignition started successfully
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The furnace failed a safety check
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The control board shut everything down
This is called a failed ignition sequence, not a random failure.
Savvy insight:
Modern furnaces don’t guess. If they shut down, something didn’t pass inspection.
🔄 How the Furnace Ignition Sequence Works (Quick & Simple)
Understanding the sequence helps you understand the shutdown.
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Thermostat calls for heat
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Inducer motor starts (clears exhaust gases)
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Pressure switch confirms proper airflow
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Igniter heats up
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Gas valve opens
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Burners light
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Flame sensor confirms flame
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Blower delivers warm air
If the furnace shuts off, it failed one of these checkpoints.
🚨 Step 1: The Flame Sensor — The #1 Reason Furnaces Light Then Shut Off
This tiny metal rod causes more panic than almost any other part.
What the Flame Sensor Does:
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Confirms that flame is present
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Sends a signal to keep the gas valve open
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Shuts gas off instantly if flame isn’t detected
Why Flame Sensors Fail:
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Light oxidation buildup (extremely common)
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Poor grounding
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Weak microamp signal
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Age-related wear
What homeowners can do safely:
If accessible and you’re comfortable:
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Turn off power
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Remove the sensor
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Gently clean with a soft cloth
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Reinstall carefully
What not to do:
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Sand aggressively
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Bend the sensor
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Bypass it (never do this)
🔗 External reference:
👉 https://www.thisoldhouse.com/heating-cooling/why-is-furnace-maintenance-important
🌬️ Step 2: Pressure Switch Problems (The Silent Shutdown)
If the furnace ignites but shuts down almost immediately—or never fully ignites—the pressure switch may be involved.
What the Pressure Switch Checks:
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Proper exhaust airflow
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Clear venting
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Safe combustion conditions
Common Causes:
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Blocked intake or exhaust pipes
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Ice, snow, or debris in PVC venting
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Cracked or loose pressure switch tubing
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Condensate backup in high-efficiency furnaces
Savvy winter tip:
After snowstorms, always inspect exterior vent pipes. Frozen vents cause countless ignition failures.
🔥 Step 3: Dirty Burners & Cross-Lighting Issues
Sometimes the furnace lights—but not correctly.
Signs of Burner Trouble:
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Flame appears uneven or delayed
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Flame “rolls” instead of spreading smoothly
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Furnace lights briefly, then shuts down
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Popping or whooshing sounds at ignition
Why This Happens:
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Dust or debris on burners
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Improper gas flow
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Misaligned burner assembly
Important:
Burner cleaning is typically a professional task due to gas safety concerns.
🧯 Step 4: Gas Supply & Gas Valve Problems
If ignition is inconsistent, gas delivery may be unstable.
What to Check Safely:
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Gas shutoff valve fully open
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Other gas appliances working normally
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No recent gas work or utility interruption
What Causes Gas-Related Shutdowns:
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Low gas pressure
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Failing gas valve
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Intermittent electrical signal to valve
Savvy warning:
Gas valve testing and replacement are never DIY tasks.
🔗 External reference:
👉 https://www.aga.org/natural-gas/safety/using-natural-gas-safely/
🌡️ Step 5: Overheating That Stops Ignition Mid-Cycle
Yes—overheating can stop ignition, too.
How This Happens:
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Restricted airflow traps heat
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High-limit switch opens
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Furnace shuts down burners
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Blower may keep running
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Furnace retries later
Common Causes:
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Dirty air filter
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Blocked vents
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Closed return grilles
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Weak blower airflow
Savvy rule:
Any ignition problem should always include an airflow check.
🔗 External reference:
👉 https://www.energy.gov/energysaver/home-heating-systems
🔌 Step 6: Control Board & Electrical Issues
Sometimes the problem isn’t mechanical—it’s electronic.
Possible Electrical Causes:
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Loose wiring connections
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Weak ground
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Faulty control board
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Inconsistent voltage supply
Signs This Might Be the Issue:
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Random shutdown timing
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Inconsistent error codes
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Furnace works intermittently
Electrical diagnosis is usually best left to a trained technician.
❄️ Step 7: High-Efficiency Furnace Condensate Problems
If you own a 90%+ efficiency furnace, ignition problems often tie back to moisture.
Watch For:
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Clogged condensate trap
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Kinked drain hose
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Water backing up into pressure switch tubing
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Frozen drain lines in winter
Any of these can interrupt the ignition sequence.
🔄 Step 8: Resetting the Furnace (One Time Only)
A reset can confirm whether the issue is temporary.
Safe Reset Steps:
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Thermostat to OFF
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Furnace power OFF for 60 seconds
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Restore power
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Set thermostat to HEAT
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Observe a full ignition attempt
If the furnace lights then dies again—stop resetting.
📞 Step 9: When to Call a Professional (No Guilt, No Delay)
Call an HVAC technician if:
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The flame appears but shuts off repeatedly
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Error codes return after cleaning the flame sensor
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You smell gas or burning odors
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Ignition failures happen multiple times per day
🧠 Savvy Final Takeaway: Ignition Failures Are Safety Successes
When your furnace lights then dies, it’s not being stubborn—it’s being smart.
Most causes come down to:
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Flame detection
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Airflow verification
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Combustion safety checks
The key is diagnosing which step failed—not forcing the furnace to keep trying.
Handled early, ignition issues are often small fixes, not system replacements.
