Goodman Furnace 3 Flashes — What It Means
3 slow flashes on a Goodman furnace control board means the pressure switch is open — the furnace’s draft inducer motor is running but the control board isn’t getting confirmation that proper combustion air pressure has been established. Without that confirmation, the furnace won’t allow ignition, so you get 3 flashes and no heat.
This code also applies to Amana furnaces and some Coleman furnaces that share the same Goodman control board platform.
The pressure switch is a small, inexpensive component — but the cause of 3 flashes is often not the switch itself. Blocked condensate drains, cracked pressure hoses, and failed inducer motors are the real culprits in most cases.
Common Causes
- Blocked condensate drain — High-efficiency (90%+) Goodman furnaces produce water vapor as a byproduct. If the condensate drain line is clogged, water backs up into the pressure switch port and holds the switch open. This is the #1 cause on 90%+ AFUE models.
- Cracked or disconnected pressure switch hose — A small rubber or vinyl tube runs from the inducer housing to the pressure switch. If it’s cracked, kinked, or has come off, the switch never sees the correct pressure.
- Failed draft inducer motor — If the inducer isn’t spinning at full speed, it doesn’t generate enough negative pressure to close the switch. Listen for weak or grinding inducer operation.
- Blocked flue or intake pipe — A bird nest, ice buildup, or debris blocking the PVC intake or exhaust pipe prevents proper draft, leaving the pressure switch open.
- Failed pressure switch — The switch diaphragm can crack or the switch contacts can fail after years of cycling.
- Blocked inducer wheel — Debris or corrosion buildup on the inducer impeller reduces draft even if the motor is spinning normally.
Step-by-Step Diagnosis {#fix}
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Listen to the inducer — When you call for heat, the inducer motor should start first (before ignition). If you hear nothing, or hear grinding/squealing, the inducer motor has likely failed. If the inducer sounds normal, proceed.
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Check the condensate drain line — On 90%+ efficiency models, locate the condensate drain tubing (usually a white PVC pipe exiting the furnace into a floor drain or condensate pump). Disconnect the drain line from the furnace and blow it out with compressed air or flush with water. A backed-up drain is the easiest fix on this list.
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Inspect the pressure switch hose — Find the small rubber tube running from the inducer housing or collector box to the pressure switch (usually a 1/4” or 3/8” hose). Check every inch for cracks, holes, or loose connections. A cracked hose is a $2 fix.
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Check the vent pipes — Go outside and look at where the intake and exhaust PVC pipes exit the building. Remove any obstructions — leaves, bird nests, ice, or debris. On horizontal runs, check for sagging that could pool condensate.
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Test the pressure switch — With the inducer running, disconnect the hose from the pressure switch port and apply gentle suction with your mouth directly to the port. If the furnace starts (indicating the switch closed), the switch itself is fine but isn’t seeing enough pressure. If nothing changes, the switch may be failed.
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Confirm switch operation with a multimeter — Power off. Disconnect the hose from the switch. With the inducer running, use a multimeter on the switch terminals — it should show continuity when you apply suction to the port. No continuity = failed switch.
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Inspect the inducer wheel — If accessible, shine a light into the inducer housing and look for debris or corrosion on the impeller blades. A dirty wheel can reduce draft enough to hold the switch open.
How to Fix It
Blocked condensate drain: Flush or blow out the entire drain line. Add a condensate drain treatment tablet to prevent future algae buildup.
Cracked pressure hose: Remove the old hose and bring it to a hardware store or order a replacement. Standard sizes are 1/4” or 3/8” ID vinyl tubing — cut to the same length and reconnect.
Failed pressure switch: Disconnect the hose and wire harness, swap in a replacement switch with the same pressure rating (marked on the switch label in inches of water column, e.g., -0.50” WC). This is a 10-minute DIY repair.
Failed inducer motor: Power off, disconnect the vent connection, remove the inducer housing bolts, and swap the motor. Match voltage and RPM from the motor label. This is a moderate DIY job.
Blocked flue: Clear the obstruction. On horizontal PVC runs that have sagged and are pooling water, add support straps to restore the correct downward pitch toward the drain.
Parts You May Need
| Part | Notes |
|---|---|
| Goodman Pressure Switch | Match pressure rating (WC value) from switch label |
| Furnace Pressure Switch Hose | 1/4” or 3/8” ID vinyl tubing — buy a few feet |
| Goodman Inducer Motor | Match voltage, RPM, and HP from inducer motor label |
| Condensate Drain Treatment | Prevents algae buildup that clogs drain lines |
| Condensate Pump | Replace if pump has failed and water is backing up |
When to Call a Technician
If you’ve checked the condensate drain, inspected the hose, cleared the vent pipes, and replaced the pressure switch — and 3 flashes continues — the inducer motor, collector box, or heat exchanger may have an internal issue. Inducer motor replacement is a manageable DIY task but requires comfortable working inside the furnace cabinet. If you’re not comfortable with that, or if there are signs of water damage or corrosion on the inducer housing, call a technician.