Troubleshooting Gas Furnace Start-Up Issues: Understanding the GR9T961005CN Logic

Y’all Ready to Light It Up? 🔥

Okay listen, nothing throws off your cozy winter vibe faster than a furnace that won't fire. You hit the heat switch, and… crickets. No click, no whoosh, no warmth. 😩

But don’t go pulling your hair out—or worse, calling for backup just yet. I’m gonna show you how to think like your furnace, read its startup logic, and troubleshoot those pesky no-heat moments step-by-step.

If you’re working with the Goodman GR9T961005CN—that’s a 96% AFUE, 100,000 BTU, two-stage gas furnace—you’re in good hands. This system is smart, efficient, and actually super communicative... if you know how to listen. 😉

Let’s dig in!

 

First: Understand the GR9T961005CN Startup Sequence 🎬

Before we fix anything, we need to understand what the correct startup sequence looks like. If you know what’s supposed to happen, then you’ll know exactly where it’s failing.

Here’s the furnace’s internal logic play-by-play:

1. Thermostat Calls for Heat

2. Draft Inducer Motor Starts

3. Pressure Switch Closes

4. Hot Surface Ignitor (HSI) Energizes

5. Gas Valve Opens

6. Ignition Occurs

7. Flame Sensor Confirms Flame

8. Blower Motor Delays On

9. Furnace Runs Until Thermostat is Satisfied

10. Blower Delays Off After Burners Shut Down

If anything in this chain fails, the system will shut down and may flash a diagnostic code via the control board.

If you're unsure what that LED is trying to tell you, Goodman has a flash code decoder guide that is chef’s kiss for techs and homeowners alike.

 

1. Thermostat Isn’t Calling for Heat 🤷🏽

We’re starting basic here.

Fixes:

• Check thermostat mode = HEAT

• Set temp at least 3–5°F above room temp

• Confirm 24V signal across W and C terminals at the furnace control board

Pro Tip: Use a jumper between R and W at the board to eliminate the thermostat as the issue.

Thermostats go bad more often than you’d think, especially those older mercury-style ones. If you're considering an upgrade, look at ENERGY STAR’s list of certified smart thermostats for efficiency and tech-savvy control.

 

2. Inducer Motor Doesn’t Start 🌀

This one’s a dealbreaker. If the inducer fan doesn’t kick on, the furnace can’t prove draft, and everything halts.

Causes:

• Failed motor

• Loose plug at control board

• Faulty relay or bad board

Fixes:

• Check for 120V to inducer when heat is called

• Confirm motor spins freely

• Listen for buzzing or humming (locked motor)

Still not sure? This HVAC School podcast episode covers inducer logic and diagnostics in the chillest way. 🎧

 

3. Pressure Switch Isn’t Closing ⚠️

Ah yes, the infamous pressure switch fail. This lil’ guy ensures the inducer is moving air out before the burners light.

Red flags:

• LED flashes pressure switch error

• System times out after ~30 seconds

• You hear inducer, but no ignition

Fixes:

• Clear any clogged condensate drains

• Check for blocked vent/exhaust

• Confirm tubing isn’t kinked or full of water

• Test with a manometer—should read around -0.5” WC when running

If the pressure switch is constantly acting up, you might be dealing with vent sizing issues. Here’s a great article on vent pipe configuration from Always Plumbing that breaks it all down.

 

4. No Glow from the Hot Surface Ignitor (HSI) 🧨

You’re halfway through the ignition sequence and… no glow. Nada. The burners never even get a shot.

Causes:

• Cracked or failed HSI

• Loose harness

• Bad relay on the board

Fixes:

• Confirm 120V to ignitor

• Carefully inspect ignitor for cracks (don’t touch the element!)

• Ohm test: Resistance should be around 40–90 ohms

If you need to replace it, go with OEM, baby. Aftermarket ignitors can be unpredictable, and we don’t do unpredictable in winter ❄️

 

5. Burners Light, Then Immediately Shut Off 🕯

This is a classic flame sensor issue. You’ll hear the whoosh of ignition, but within 1–2 seconds, the gas shuts off.

Why? The board isn’t sensing the flame, so it thinks there’s danger.

Fixes:

• Turn off power

• Remove the flame sensor

• Polish it with steel wool or emery cloth

• Reinstall, ensuring good electrical contact

Still having issues? Check the microamp signal. You want 1.0 μA or more. Use your meter in microamp mode in series with the sensor wire.

This short Transmitter Shop explainer has some bonus info on flame failure and relays.

 

6. Blower Doesn’t Turn On 🤯

Everything else works, burners stay lit, but there’s no airflow. We’re talkin’ hot heat exchanger, zero circulation. This is dangerous—heat rise gets out of control fast.

Fixes:

• Check blower delay setting on control board (usually 30–60 seconds)

• Confirm blower capacitor is healthy (if PSC motor)

• Check for flashing high-limit code

Also, make sure return air filters aren’t blocked. A clogged filter can send your heat exchanger temps soaring—and trip the high limit. Not fun.

 

7. It Runs, But Then Locks Out 😵

Everything seems fine, but after a few minutes, the system shuts off with a blink-blink error.

You may be in soft lockout due to:

• Repeated ignition failures

• Flame dropout

• Limit switch cycling

Fixes:

• Clean flame sensor again

• Check for draft interruptions

• Confirm limit switch continuity with a meter

• Monitor voltage dips—low voltage can cause ghost issues

Need a techier resource? HVAC Know It All wrote a great blog on furnace lockout causes and resets.

 

Bonus: Diagnostic Code Reference 💡

The GR9T961005CN flashes codes right on the control board. Here's what they usually mean:

• 1 Flash: No ignition

• 2 Flashes: Pressure switch stuck closed

• 3 Flashes: Pressure switch stuck open

• 4 Flashes: Limit switch open

• 6 Flashes: Flame sensor failure

• 7 Flashes: Rollout switch open

Don’t guess—read the legend on the inside of the furnace door. It’s your cheat sheet.

 

Final Checklist from Savvy 

Before walking away from a furnace startup, here’s my Fab Five:

1. Confirm burner ignition sequence completes

2. Verify blower delay & speed settings

3. Check all limit switches & safeties

4. Monitor flame signal

5. Run system through 2–3 cycles to confirm stability

And babe, don’t forget to log everything. You never want to be the tech who can’t remember if the gas pressure was 3.2" or 4.0". 😬

 

From No Heat to Heat Queen 👑

Troubleshooting the Goodman GR9T961005CN is all about understanding the sequence. Once you know what’s supposed to happen, it’s easy to zero in on what’s not.

So next time your furnace throws a tantrum, just channel your inner Savvy—grab your meter, trust the logic, and fix it with flair 💅

Need the full matched system with condenser and coil too? Grab it right now from The Furnace Outlet and keep your installs stress-free.

Curious about handling refrigerant in this combo? Visit my guide: How to Handle R-32 Refrigerant Safely in the GLXS4BA3610, CAPTA3626C3, and GR9T961005CN.

Until next time, stay warm, stay wonderful, and stay wildly competent.
— Savvy Mavi 🔥