If your furnace lights for a few seconds, shuts off, tries again… and repeats that dance until it locks out — congratulations. You’ve met one of the most misunderstood parts in HVAC:
👉 The flame sensor.
This tiny metal rod causes more “my furnace is broken” panic than almost any other component. And the kicker?
100,000 BTU 96% AFUE Upflow/Horizontal Two Stage Goodman Gas Furnace - GR9T961004CN
Most flame sensor problems aren’t failures — they’re maintenance issues.
Let’s talk about what the flame sensor actually does, why it gets “funky,” and how to clean it the right way so you don’t make things worse.
🧠 What the Flame Sensor Actually Does (Simple, Honest Explanation)
The flame sensor has one job:
👉 Prove that flame exists after ignition.
Here’s the sequence:
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Furnace ignites burners
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Flame sensor detects flame via electrical current
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Control board says, “Good — keep the gas flowing”
If the sensor doesn’t prove flame within a few seconds, the furnace shuts the gas off for safety.
No proof = no heat.
🚨 Classic Signs of a Dirty Flame Sensor
If you notice any of these, the flame sensor jumps to the top of the suspect list:
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Furnace lights, then shuts off after 2–5 seconds
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Repeats ignition attempts
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Eventually locks out
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Error code indicating ignition failure (often 6 flashes on Goodman)
Jake’s shortcut:
If it lights briefly, the gas valve works. The sensor just isn’t confirming flame.
🧪 Why Flame Sensors Get Dirty (Even in New Furnaces)
Flame sensors don’t fail easily — but they get coated.
Common causes:
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Normal combustion byproducts
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Dust in the burner area
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New installation residue
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Slight condensation exposure
High-efficiency furnaces are especially prone because they run cooler and longer.
🔗 Ignition & flame sensing overview:
https://www.partshnc.com/blog/goodman-furnace-troubleshooting-guide
🔍 Where the Flame Sensor Is (And What It Looks Like)
Most flame sensors:
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Are a thin metal rod
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Mounted near the burner assembly
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Held in place by one screw
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Have one wire attached
It’s not the igniter.
It’s not the gas valve.
It’s the simplest-looking part that causes the biggest headache.
🧰 What You’ll Need (Keep It Simple)
You don’t need a toolbox full of gadgets.
✔ Screwdriver
✔ Fine abrasive pad or steel wool (very fine)
✔ Clean paper towel
✔ Steady hands
❌ No sandpaper
❌ No wire brushes
❌ No chemicals
Jake’s rule:
If it removes metal, it’s too aggressive.
🧼 How to Clean a Flame Sensor (The RIGHT Way)
Step-by-step:
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Turn off power to the furnace
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Remove the flame sensor screw
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Gently pull the sensor straight out
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Lightly polish the metal rod
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Wipe clean — no residue
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Reinstall firmly (not overtightened)
That’s it.
🔗 Manufacturer maintenance guidance:
https://www.goodmanmfg.com/resources/hvac-learning-center
🚫 How Homeowners Accidentally Ruin Flame Sensors
I see this all the time.
Don’t do these:
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Sanding aggressively
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Scraping with a knife
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Using brake cleaner or solvents
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Touching the rod with greasy fingers
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Bending the rod during cleaning
Once the surface coating is damaged, the sensor may never read correctly again.
Jake’s warning:
Clean ≠ grind. Gentle wins every time.
🔁 How Often Flame Sensors Need Cleaning
There’s no universal schedule — but here’s real-world guidance:
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Once a year is common
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Dusty homes may need it more often
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New installs often need first-year cleaning
🔗 Annual furnace maintenance overview:
https://www.energy.gov/energysaver/furnaces-and-boilers
If you’re cleaning the sensor multiple times per season, something else is wrong.
🔄 When Cleaning Is NOT Enough
Sometimes cleaning doesn’t fix it.
Possible reasons:
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Cracked porcelain insulator
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Weak microamp signal
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Poor grounding
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Control board issue
At that point, replacement or professional diagnosis is the smart move.
🔗 Flame sensor diagnostics explanation:
https://hvacoptimizer.net/goodman-furnaces-troubleshooting/
⚡ The Hidden Issue: Grounding Problems
Flame sensors rely on microamps — tiny electrical signals.
Loose grounds, corroded connections, or painted burner surfaces can interrupt that signal even if the sensor is clean.
Jake’s insight:
A perfect flame sensor still fails if the circuit can’t complete.
🚫 What NOT to Do to “Test” a Flame Sensor
Let’s clear this up.
❌ Don’t bypass it
❌ Don’t tape wires
❌ Don’t jump terminals
❌ Don’t keep resetting the furnace
These tricks don’t fix the issue — they just delay the shutdown.
🔗 Furnace safety basics (CDC):
https://www.cdc.gov/carbon-monoxide/about/index.html
📞 When to Call a Professional
Call a licensed tech if:
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Cleaning didn’t solve the issue
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Flame sensor failures repeat frequently
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Furnace locks out after multiple attempts
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You see error codes beyond ignition failure
🔗 Find Goodman-authorized service:
https://www.goodmanmfg.com/support/find-a-dealer
🧠 Jake’s Flame Sensor Quick Checklist
✔ Furnace lights briefly, then shuts off
✔ Gas supply confirmed
✔ Flame sensor cleaned gently
✔ Sensor reinstalled correctly
✔ No repeated lockouts
If all five check out, you’ve done your part.
🏁 Final Word from Jake
The flame sensor isn’t fragile — but it demands respect.
Clean it the right way, at the right time, and it’ll quietly do its job for years.
Rush it. Scrape it. Ignore it.
And it’ll shut your furnace down every single time — without apology.
Diagnose first. Clean gently. Replace only when proven.
