Goodman Furnace 3 Blinks? How to Fix the ‘Pressure Switch’ Error

The house is cold. The thermostat is calling for heat. You hear the furnace start to rumble. The small exhaust fan hums to life. You wait for the “whoosh” of the burners igniting, but it never comes. Instead, the system shuts down, waits a few seconds, and tries again.

If you look through the small glass viewport on the bottom door of your Goodman furnace, you likely see a red LED light flashing in a specific pattern: Three flashes, a pause, and three flashes again.

This is one of the most common fault codes in the HVAC world. It indicates a Pressure Switch Stuck Open error.

While “Pressure Switch” sounds complicated, it is actually a simple safety sensor. It is telling you that the furnace does not believe it is safe to light the fire because it cannot confirm that the exhaust gases are leaving the house.

This guide explains exactly why your Goodman furnace is throwing this code, how to verify if the “inducer motor” is working, and how to use a simple paperclip to fix a common design flaw that plagues these units.

Decoding the ‘Pressure Switch Stuck Open’ Error

To fix the problem, it is necessary to understand how a modern gas furnace breathes.

Before a furnace lights the gas burners, it must prove that the chimney (flue pipe) is clear. To do this, it turns on a small electric fan called the Draft Inducer Motor. This motor creates suction (negative pressure) inside the heat exchanger.

The Pressure Switch is a small, round safety device connected to that motor by a rubber hose. Inside the switch is a delicate diaphragm. When the inducer motor spins up, the suction pulls the diaphragm closed, completing an electrical circuit.

The Logic

• Switch Closed: The flue is clear. Safe to light fire.
• Switch Open (3 Blinks): No suction detected. The flue might be blocked, or the motor is dead. The system locks out to prevent Carbon Monoxide from filling the home.

Is the Inducer Motor Running?

The first step in troubleshooting a 3-blink error is to listen to the furnace.

Turn the thermostat up to call for heat. Stand next to the unit.

1. Silence: If you hear a click from the thermostat but the furnace makes absolutely no noise, the issue is electrical (power, control board, or thermostat).
2. Humming: If you hear a loud buzzing or humming noise but no fan spinning, the inducer motor is seized or has a bad capacitor.
3. Running: If you hear the small fan spinning smoothly, but the fire never lights, the motor is working. This means the problem is with the Pressure Switch, the Tubing, or a Blockage.

If the motor is running but not firing, proceed to the checks below. For more on ignition sequences, refer to Furnace Starts Then Stops.

Blocked Exhaust Vents

In the autumn, this is the most frequent cause of a “Stuck Open” pressure switch.

Goodman furnaces, especially high-efficiency models, vent through white PVC pipes that stick out of the side of the house or the roof. These pipes are warm and cozy places for wildlife.

Common Blockages:

• Wasps and Bees: Insects often build nests inside the open pipe termination during the summer.
• Leaves: Debris can fall into roof vents.
• Snow/Ice: In winter, drifting snow can cover the intake or exhaust pipes.

If the pipe is blocked, the inducer motor runs, but it cannot create enough suction to close the switch. Go outside and visually inspect the pipes. Clear any debris with a long stick or a shop vac.

Clogged Condensate Trap (High Efficiency Models)

If your Goodman furnace has white PVC venting, it is a “Condensing Furnace” (90%+ efficiency). This means it pulls so much heat out of the exhaust gas that the gas turns back into liquid water.

This water drains out through a specialized trap and hose system.

If that drain trap gets clogged with slime or algae, the water backs up. It fills the inducer motor housing until it covers the pressure port. The sensor cannot feel the suction through the water.

The Test

Locate the white plastic drain trap inside the furnace. Remove it (have a bucket ready). Shake it. If it is heavy and full of gunk, wash it out in a sink with hot water.

The ‘Paperclip Trick’ (Cleaning the Port)

On many Goodman units, the pressure switch itself is not broken. The hose is not broken. The drain is clear. The problem is a tiny design flaw in the metal casting of the inducer motor housing.

The rubber hose from the pressure switch connects to a small nipple (port) on the inducer fan. Over time, rust, calcium, and combustion byproducts build up inside this tiny port, blocking the air signal.

The Fix

1. Turn off power to the furnace.
2. Pull the black rubber hose off the small port on the inducer motor.
3. Straighten a standard paperclip.
4. Gently poke the paperclip into the metal port. Move it in and out to break up the crusty blockage.
5. Reattach the hose.
6. Turn the power on.

Technicians often find that this simple cleaning restores the suction signal immediately.

Goodman Diagnostic Code Cheat Sheet

While 3 blinks is the most common, Goodman furnaces use a variety of flash codes.

Flashes	The Meaning	The Likely Fix
Steady On	Internal Control Failure	Replace Circuit Board
1 Blink	Ignition Failure (Lockout)	Clean Flame Sensor
2 Blinks	Pressure Switch Stuck Closed	Replace Pressure Switch
3 Blinks	Pressure Switch Stuck Open	Check Vent / Inducer / Port
4 Blinks	High Limit Open (Overheat)	Change Dirty Air Filter
Rapid Flash	Reversed Polarity	Check Electrical Wiring

FAQ

Can I bypass the pressure switch to get heat?

No. Never bypass a safety switch. If you jumper the switch, you are forcing the furnace to run even if the exhaust flue is blocked. This can pump deadly Carbon Monoxide into your bedrooms.

How do I reset my Goodman furnace?

Turn the thermostat to OFF. Locate the power switch (light switch) on the side of the furnace or the circuit breaker in the panel. Turn it OFF for 30 seconds. Turn it back ON to reset the control board logic.

Why is there water in my pressure switch hose?

Water in the hose indicates a drainage failure. The condensate trap is clogged, or the drain lines are routed incorrectly (uphill). Water blocks the air signal, causing the switch to flutter or stay open.

Conclusion

A 3-blink error on a Goodman furnace is a request for airflow. The system is trying to breathe, but something – a wasp nest, a clogged drain, or a rusty port – is stopping it.

1. Check the Vents: Ensure the outdoor pipes are clear.
2. Check the Drain: Clean the condensate trap.
3. Clean the Port: Use the paperclip trick.

If the inducer motor is humming but not spinning, or if the pressure switch remains open despite a clear path, the component has likely failed. Electrical testing is required to verify the motor capacitor and switch resistance.

For professional diagnostics and Furnace Services, contact our team to ensure your home stays warm and safe.