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Troubleshooting Guide: Common Problems With Goodman 96% Furnaces

Goodman 96% furnaces—GM9S96, GMEC96, GMVC96, GMSS96, GCVM96, and their Daikin/Amana equivalents—are excellent high-efficiency units, but they’re not magical. They still run into issues: blocked vents, pressure switch faults, flame sensor problems, clogged drains, blower failures, lockout conditions, and wiring faults.

This guide is your no-nonsense, Practical Jake troubleshooting manual. It tells you what a homeowner can safely check, what each common error code means, and which problems require a trained technician immediately.

But let’s be crystal clear:
This is not a DIY repair guide for tasks that require tools, gas work, electrical skills, or opening sealed compartments. I’ll tell you what’s safe, what’s not, and when to stop and call a tech.

If you stick to the safe actions here, you’ll avoid 80% of unnecessary service calls. If your system has a deeper problem, you’ll know exactly what to tell a technician so they fix it faster and cheaper.

1. Quick Fixes Homeowners Can Safely Try

Here’s what you CAN do without special tools or risking damage:

✔ Replace or check the furnace filter

A dirty filter is the #1 cause of limit trips, airflow issues, and loud operation.

Replace filters every 1–3 months.
Make sure it's pointed with airflow arrow toward furnace.
Never run the furnace without a filter.

✔ Check the thermostat

Things homeowners overlook:

Heat mode ON
Fan set to AUTO
Batteries replaced (if applicable)
Set temperature above room temp
No schedule overriding heat
Thermostat not stuck in “cooling lockout” after power cycle

✔ Check power switches

Your Goodman 96% has two on/off controls:

Furnace service switch (looks like a light switch)
Breaker at electrical panel

Make sure both are on.

✔ Check the furnace door

The Goodman has a safety door switch. If the panel is loose or slightly ajar, the furnace will not run.

✔ Cycle power to reset error codes

Turn furnace switch OFF → wait 30 seconds → turn ON.

This often clears pressure switch momentary trips or soft faults.

✔ Check outdoor intake & exhaust pipes

96% furnaces use PVC pipes. Make sure:

No snow, leaves, or debris blocking them
No dead animals (yes, it happens)
No ice buildup around the exterior termination
No wasp nests or spiderweb blockages

✔ Inspect the condensate drain (visually only)

Look for:

Water backing up
Drain tubing sagging
Drain pump stuck or full
Freeze potential in winter

Do not open or remove the trap unless trained.

✔ Listen for blower operation

If the blower never starts, that’s important info for diagnostics.

✔ Check household vents

Closed vents cause airflow problems, overheating, limit trips, and pressure-switch faults.

Open at least 80% of all supply registers.

✔ Make sure gas supply valve is open

Only visually confirm the handle is parallel with the pipe. Do NOT touch gas fittings.

2. Goodman 96% Furnace Error Code Explanations

Codes vary slightly by motherboard generation, but common ones are consistent across the GMVC/GM9/GMEC/GCVC families.

Here’s a practical breakdown:

1 Flash (or rapid continuous flash):

Ignition failure / no flame detected.

Common causes:

Dirty flame sensor
Weak flame signal
Low gas pressure
Ignitor failure
Clogged burners

Homeowner action: check filter, reset power, clear vents, and proceed to flame sensor cleaning (later section).

2 Flashes:

Pressure switch stuck open.

Meaning the furnace does not see enough draft or airflow to begin ignition.

Common causes:

Blocked intake/exhaust
Condensate blockage
Cracked or disconnected pressure tubing
Bad inducer
High static pressure
Dirty filter
Vent icing

Homeowner action: check filter and vent pipes for blockage, then reset.

3 Flashes:

Pressure switch stuck closed.

This means the switch is closed BEFORE the inducer starts—incorrect sequence.

Common causes:

Pressure tubing full of water
Switch welded shut
Blockage creates vacuum in venting
Miswiring
Bad circuit board

Homeowner action: check drain, check vents.

4 Flashes:

Open high-limit switch.

Meaning the furnace overheated.

Common causes:

Dirty filter
Blocked vents
Closed registers
Blower malfunction
Low airflow due to duct restriction
Oversized furnace short-cycling

Homeowner action: replace filter, open vents, check blower noise.

5 Flashes:

Flame sensed when no flame should be present.

Common causes:

Flame sensor short
Gas valve leaking (dangerous—call technician immediately)
Control board fault
Grounding issues

Homeowner action: turn furnace OFF and call a pro.

6 Flashes:

Rollout switch open.

This one is serious.

Common causes:

Burner flame rollout
Cracked heat exchanger
Blocked or collapsed inducer or vent
Rollout switch failure (rare)

Homeowner action:
Turn the furnace OFF immediately. Do not reset more than once. Call a technician.

7 Flashes:

Low flame signal.

Often caused by a dirty flame sensor.

8 Flashes:

Ignitor circuit failure.

Likely defective ignitor or wiring.

For a reference to common Goodman codes, this resource helps:
Goodman_Error_Code_Reference

3. Flame Sensor Cleaning Steps (Safe, Homeowner-Level)

Goodman 96% furnaces trip frequently due to dirty flame sensors. Cleaning them is safe if you do it carefully.

Tools needed: fine steel wool or Scotch-Brite pad, Phillips screwdriver.

Steps:

Turn furnace power OFF with the switch.
Remove the blower door.
Locate the flame sensor (thin metal rod near the burner, with one wire).
Remove the single mounting screw.
Gently buff ONLY the metal rod with steel wool—don’t bend anything.
Wipe dust with a clean cloth.
Reinstall sensor and tighten screw.
Restore power and run furnace.

Do NOT use sandpaper. It scratches the surface and reduces lifespan.

More detail:
Flame_Sensor_Cleaning_Guide

4. Pressure Switch Problems (Open vs Closed Symptoms)

Pressure switches protect the furnace from unsafe venting or combustion conditions. Goodman 96% units rely heavily on them.

Pressure Switch Stuck OPEN – Symptoms

Error: 2 flashes
Furnace begins startup but shuts down
Inducer running but no flame
You may hear click-click-click
Common causes:
- Blocked intake/exhaust
- Dirty filter
- Drain clog
- Inducer wheel dirty or weak
- Venting slope incorrect
- Pressure tube waterlogged

Homeowner fixes:

Replace filter
Clear snow/ice at PVC pipes
Ensure the condensate drain is flowing
Reset furnace

Pressure Switch Stuck CLOSED – Symptoms

Error: 3 flashes
Furnace will NOT start inducer
Switch reads “closed” too soon
Common causes:
- Venting blockage causing vacuum
- Pressure tubing connected wrong
- Faulty switch
- Control board problem

Homeowner fixes:

Inspect vents and drain lines
Reset furnace
If codes persist, tech is required

Great background reading:
Pressure_Switch_Troubleshooting

5. Blocked Intake/Exhaust Problems (Very Common in 96% Furnaces)

Goodman 96% furnaces rely on PVC intake and exhaust pipes. Anything that blocks airflow can shut your unit down instantly.

Common signs:

Furnace runs for 10–30 seconds then stops
Pressure switch error codes (2 or 3 flashes)
Water gurgling in vent
Frost or ice on exterior termination
Wind-driven snow plugging intake
Soot or water dripping from PVC joint
Inducer sounds louder than normal

Causes:

Snow drifts
Rodents
Leaves
Spider webs
Wasp nests
Ice buildup (very common in northern states)
Vent sagging and holding water

Homeowner fixes:

Clear snow
Remove visible debris
Pour warm—not hot—water around frozen terminations
Make sure the termination vent is at the correct height above ground

For more examples:
Blocked_Vent_Symptoms

6. Drain Blockage Symptoms (Critical on 96% Condensing Furnaces)

Your Goodman 96% generates a LOT of water. If the condensate drain clogs, the furnace will shut down to protect itself.

Symptoms:

Furnace starts then stops
Water pooling inside furnace
Water around furnace base
Gurgling or bubbling sounds
Pressure switch errors
Blower runs but no heat
Drain tube full of water
Furnace runs only with the door cracked open (unofficial sign of blocked pressure tubing)

Causes:

Slime/algae in drain
Blocked external drain line
Sagging tubing holding water
Frozen drain line
Internal trap blockage
Cracked condensate pan (less common)

Homeowner-safe steps:

Inspect visually (don’t disassemble traps)
Ensure drain tubing slopes downward
Make sure drain pump (if installed) is plugged in
Empty the pump reservoir if full
Clear debris from the drain termination

For deeper drain best practices:
Condensate_Drain_Education

7. Blower Failure Signs (ECM or PSC Motor Issues)

Goodman 96% units typically use ECM blowers (variable-speed or constant torque). When these fail, symptoms are distinct.

Symptoms of a failing blower motor:

No air from vents even though furnace ignites
Furnace overheats and shuts down (error 4 flashes)
Blower tries to start then stops
Loud humming or vibration
Burning smell (turn off immediately)
Erratic speeds
Motor runs constantly even with thermostat off (control board issue)

Causes:

Failed ECM module
Failed motor windings
Bad capacitor (PSC motors only)
Loose wiring harness
Control board failure
High static pressure from duct problems

Homeowner actions:

Replace the air filter
Ensure supply/return vents fully open
Reset the furnace
Listen for the blower startup sequence

But blower diagnosis beyond that is technician-level.

For general blower motor understanding:
Blower_Motor_Troubleshooting

8. When You MUST Call a Technician

I’m Practical Jake—but even I draw hard lines. Here’s when you stop and call a pro.

✔ Gas smell of ANY kind

Shut furnace OFF and call the gas company or emergency service. Do not troubleshoot.

✔ Rollout switch trip (error 6 flashes)

Possible cause: cracked heat exchanger
This is not DIY territory.

✔ Flame present when it shouldn’t be (error 5 flashes)

Dangerous condition—requires professional diagnostic.

✔ Repeated pressure switch faults after checking vents

This means deeper issues:

Venting design faults
Condensate trap clog
Compromised draft inducer
Failed pressure switch

✔ Water leaking inside the furnace cabinet

This could ruin your board or blower motor.

✔ Electrical burning smell

Turn off immediately.

✔ Furnace short-cycles repeatedly

Often caused by sizing, ductwork, or safety-limit issues.

✔ Control board errors or wiring issues

Homeowners should never attempt electrical repairs.

✔ Blower fails to start after reset

Could be an ECM module failure.

✔ You cleaned the flame sensor, but ignition still fails

This means:

Ignitor may be weak
Gas valve failing
Burner alignment issues
Low gas pressure

✔ Any work involving:

Gas valve
Ignitor replacement
Pressure switch replacement
Vent redesign
Control board
Heat exchanger inspection
Combustion or CO analysis

All of these are professional-only repairs.

Conclusion

A Goodman 96% furnace is a workhorse—but like any high-efficiency system, it relies on clean airflow, proper drainage, safe venting, and reliable sensors. Most homeowner-friendly troubleshooting involves: